Electron beam inspection system and inspection method and method of manufacturing devices using the system

ABSTRACT

An electron beam inspection system of the image projection type includes a primary electron optical system for shaping an electron beam emitted from an electron gun into a rectangular configuration and applying the shaped electron beam to a sample surface to be inspected. A secondary electron optical system converges secondary electrons emitted from the sample. A detector converts the converged secondary electrons into an optical image through a fluorescent screen and focuses the image to a line sensor. A controller controls the charge transfer time of the line sensor at which the picked-up line image is transferred between each pair of adjacent pixel rows provided in the line sensor in association with the moving speed of a stage for moving the sample.

BACKGROUND OF THE INVENTION

The present invention relates to an inspection system for inspecting anobject, e.g. a wafer, by using an electron beam to detect a defect orthe like in a pattern formed on the surface of the sample underinspection. More particularly, the present invention relates to aninspection system and inspection method wherein an electron beam isirradiated to the surface of an object under inspection, and image datais obtained from the number of secondary electrons emitted from thesample surface, which varies according to the properties of the samplesurface, and a pattern or the like formed on the sample surface isinspected with high throughput on the basis of the image data, as in thecase of detecting defects on a wafer in the semiconductor fabricationprocess. The present invention also relates to a method of fabricatingdevices at high yield by using the inspection system.

Semiconductor fabrication processes are going to enter a new era wheredesign rules are 100 nm. The form of production is shifting from limitedlarge-lot production, represented by the fabrication of DRAMs, todiverse small-lot production as is the case with SOC (Silicon On Chip).As a result, the number of production steps has increased, and it hasbecome essential to improve the yield for each production step.Consequently, the inspection for process-induced defects has becomeimportant. Conventionally, a wafer defect inspection is performed aftereach step of the semiconductor manufacturing process. With the progressof the technology to fabricate high-integration semiconductor devicesand to form small and fine patterns, a high-resolution andhigh-throughput defect inspection system has been demanded. The reasonfor this is that a resolution of 100 nm or below is required to detectthe defects on a wafer substrate fabricated with 100 nm design rules. Inaddition, as the degree of integration of semiconductor devicesincreases, the number of production steps increases, resulting in anincrease in the number of inspections to be performed. For this reason,high throughput is demanded. Further, as the number of layersconstituting semiconductor devices increases, it is required that thedefect inspection system should have the function of detecting contactfailures (electrical defects) of vias for connection between wiringpatterns on different layers.

As this type of defect inspection system, an optical defect inspectionsystem has heretofore been used. However, the optical defect inspectionsystem is limited in its resolution capability. That is, the resolutionis limited to ½ of the wavelength of light used. In a practical exampleusing visible light, the resolution is of the order of 0.2 μm. Thus, theoptical defect inspection system cannot meet the resolutionrequirements. Further, the optical defect inspection system cannotperform inspection for electrical conduction failures (opens, shorts,etc.), that is, contact failures occurring in semiconductor devices.

Under these circumstances, a defect inspection system using an electronbeam has recently been developed for use in place of the optical defectinspection system.

In such an electron beam type defect inspection system, a scanningelectron microscope system (SEM system) has generally been put topractical use. The inspection system exhibits a relatively highresolution, i.e. 0.1 μm, and is capable of inspection for electricaldefects (disconnection and conduction failures of wiring patterns,conduction failures of vias, etc.). In the defect inspection systemmaking use of SEM, however, the amount of beam current and the responsespeed of the detector are limited. Therefore, a great deal of time isrequired to perform defect inspection. For example, it takes 8 hours toinspect one wafer (20-cm wafer). Thus, the inspection time is extremelylong. Accordingly, the throughput (the number of wafers inspected perunit time) is unfavorably low in comparison to other process systemssuch as optical defect inspection systems. In addition, the electronbeam type defect inspection system is very costly. Accordingly, it isdifficult to use it after each step of the semiconductor fabricationprocess. In the present state of the art, the electron beam type defectinspection system is used after an important process step, e.g. afteretching, film deposition (including copper plating), or CMP(Chemical/Mechanical Polishing) planarization treatment.

The defect inspection system using the scanning electron microscopesystem (SEM system) will be described below in more detail. In thedefect inspection system, an electron beam is focussed (the focussedbeam diameter corresponds to the resolution) and a sample, e.g. a waferis linearly irradiated so as to be scanned with the focussed electronbeam. Meanwhile, a stage having the wafer placed thereon is moved in adirection perpendicular to the electron beam scanning direction, wherebyan observation region on the wafer is irradiated planarly with theelectron beam. The scanning width of the electron beam is generallyseveral 100 μm. By the irradiation with the focussed electron beam(referred to as “primary electron beam”), secondary electrons areemitted from the wafer. The secondary electrons are detected with adetector (a scintillator+a photomultiplier) or a semiconductor typedetector (a PIN diode type detector), for example. The coordinates ofthe position of irradiation with the electron beam and the number ofsecondary electrons (signal intensity) are combined to produce an image.Image data thus obtained is stored in a storage unit. Alternatively, theimage can be output onto a CRT (Cathode-Ray Tube). The foregoing is theprinciple of the SEM (Scanning Electron Microscope). From the imageobtained by this method, possible defects on the in-processsemiconductor (Si, in general) wafer are detected. The inspection speed(corresponding to the throughput) is determined by the amount of theprimary electron beam (electric current value), the beam diameter, andthe response speed of the detector. The present maximum values of thesefactors are as follows. The beam diameter is 0.1 μm (this may beregarded as equal to resolution). The electric current value is 100 nA.The response speed of the detector is 100 MHz. In this case, it takesabout 8 hours to inspect one wafer having a diameter of 20 cm, as hasbeen stated above. Thus, the scanning electron beam type defectinspection system suffers from a serious problem that the inspectionspeed is extremely lower ( 1/20 or less) than those of other processsystems such as optical defect inspection systems.

The present invention was made in view of the above-described problems.Accordingly, an object of the present invention is to improve theinspection speed for detecting defects on a sample, e.g. a wafer.

SUMMARY OF THE INVENTION

The present invention relates to a defect inspection system utilizing animage projection system using an electron beam as a method for improvingthe inspection speed of the scanning electron beam (SEM) type defectinspection system. The image projection system will be described below.

In the image projection system, an observation region of a sample isirradiated with a primary electron beam by one shot (i.e. apredetermined area is irradiated with the electron beam withoutperforming scanning), and secondary electrons emitted from theirradiated region are collectively focused onto a detector (amicrochannel plate+a fluorescent screen) as an electron beam image by alens system. The image thus formed is converted into an electric signalby a two-dimensional CCD (Charge-Coupled Device; solid-state imagepickup device) or a TDI (Time Delay Integration)-CCD (i.e. a line imagesensor) and output onto a CRT or stored in a storage unit as imageinformation. From the image information, possible defects on the samplewafer [in-process semiconductor (Si) wafer] are detected. In the case ofCCD, the travel direction of the stage is the minor axis direction (ormay be the major axis direction), and the stage is moved in astep-and-repeat manner. In the case of TDI-CCD, the stage is movedcontinuously in the integration direction. Because it allows images tobe obtained continuously, TDI-CCD is used to perform defect inspectioncontinuously. The resolution is determined by the magnification,accuracy and so forth of the image projection optical system (secondaryoptical system). In a certain experimental example, a resolution of 0.05μm was obtained. In the experimental example, when the resolution wasset to 0.1 μm and electron beam irradiation conditions were set so thatthe size of an inspection region on a wafer was 200 μm by 50 μm and theamount of the primary electron beam (electric current value) was 1.6 μA,the inspection time was of the order of 1 hour per 20-cm wafer. In otherwords, the image projection system provides an inspection speed 8 timesas high as that obtained by the SEM system. It should be noted that thespecifications of TDI-CCD used in the experimental example were asfollows. The number of pixels was 2048 pixels×512 rows, and the linerate was 3.3 μs (line frequency: 300 kHz).

The irradiation area (planar dimension) in this example was set inconformity to the specifications of the TDI-CCD. However, theirradiation area may be changed according to the object to beirradiated.

The following is the outline of an electron beam inspection systemutilizing the image projection system.

The electron beam inspection system includes a primary electron opticalsystem for shaping an electron beam emitted from an electron gun into adesired configuration (e.g. a rectangular or elliptical configuration)and irradiating the shaped electron beam to the whole area of anobservation region on the surface of a sample (e.g. a wafer or a mask;hereinafter occasionally described as a wafer) to be inspected. Theelectron beam inspection system also includes a secondary electronoptical system directs secondary electrons emitted from the wafer towarda detector. The detector converts the secondary electrons into anoptical image and forms an image of the wafer. The electron beaminspection system further includes a controller for controlling thedetector. The primary electron optical system has an electron gun foremitting an electron beam, and a primary electrostatic lens system forshaping the electron beam into a beam having a predetermined sectionalconfiguration. The primary electron optical system is disposed at apredetermined angle to a direction perpendicular to the surface of thewafer. The constituent elements of the primary electron optical systemare placed in series with the electron gun positioned at the top.Between the primary electron optical system and the secondary electronoptical system, an E×B deflector (also known as “Wien filter” or “E×Bseparator”) is disposed along a direction perpendicular to the surfaceof the wafer to deflect the electron beam and to separate the secondaryelectrons from the wafer by a field where an electric field and amagnetic field perpendicularly intersect each other. The secondaryelectron optical system has a secondary electrostatic lens systemdisposed to extend in a direction perpendicular to the wafer surfacealong the optical axis of the secondary electrons from the wafer, whichare separated by the E×B separator, from the primary electron opticalaxis to deflect and focus the secondary electrons.

As the electron gun, a thermal electron beam source type is used, inwhich electrons are emitted by heating an emissive material (cathode).Lanthanum hexaboride (LaB₆) is used as the emissive material (emitter)as a cathode. It is also possible to use other materials, provided thatthey have a high melting point (the vapor pressure at high temperaturesis low) and a low work function. A cathode of lanthanum hexaboride(LaB₆) having a truncated conical tip is used. It is also possible touse a frustoconical cathode, i.e. a truncated cone-shaped cathode. Thediameter of the truncated tip of the cathode is of the order of 100 μm.There are other electron beam sources available, i.e. a field emissiontype electron beam source and a thermal field emission type electronbeam source. However, a thermal electron beam source using LaB₆ is mostsuitable for use in a system in which a relatively wide region (e.g. 100by 25 to 400 by 100 μm²) is irradiated with a large electric current (ofthe order of 1 μA) as in the case of the present invention. It should benoted that the SEM system generally uses a thermal field emission typeelectron beam source. It is a matter of course that a field emissiontype electron beam source or a thermal field emission type electron beamsource may be used in this embodiment in place of thermal electron beamsource. The thermal field emission type electron beam source is a systemin which electrons are emitted by applying a high electric field to anemissive material, and the emission of electrons is stabilized byheating its electron beam emitting part.

The primary electron optical system constitutes a part that forms aprimary electron beam emitted from an electron gun and shapes theprimary electron beam into a desired configuration, e.g. a rectangularor circular (elliptical) configuration, and further irradiates therectangular or circular (elliptical) primary electron beam to the wafersurface. The beam size and current density of the primary electron beamcan be controlled by controlling the conditions of lenses provided inthe primary electron optical system. The E×B filter (Wien filter)provided at the joint between the primary and secondary electron opticalsystems can change the course of the primary electron beam so that it isincident perpendicularly or normally on the wafer surface.

The electron gun is further provided with a Wehnelt, triple anode lensand a gun aperture. Thermal electron emitted from the cathode formedfrom LaB₆ are focused through the Wehnelt and triple anode lens onto thegun aperture as a crossover image.

The primary electron optical system is further provided with a fieldaperture for optimizing the area of the primary electron beam on thewafer, together with an NA aperture. The primary electron beam whoseangle of incidence on the lens has been optimized by the field apertureis focussed by the primary electrostatic lens system to form a lightcrossover image at the NA aperture before being planarly irradiated tothe wafer surface. The second stage of the primary system electrostaticlens comprises quadrupole lenses (QL) arranged in three stages and oneaperture aberration correcting electrode. Quadrupole lenses requirestrict alignment accuracy but exhibit strong focussing action incomparison to rotationally symmetric lenses. The aberration of thequadrupole lenses, which correspond to the spherical aberration ofrotationally symmetric lenses, can be corrected by applying anappropriate voltage to the aperture aberration correcting electrode.Thus, a uniform planar beam can be applied to a predetermined region onthe wafer surface.

The secondary electron optical system has an electrostatic lens (CL) andan intermediate lens (TL), which correspond to an projector, a fieldaperture (FA), and a second-stage lens (PL) provided on the detectorside of the field aperture position. Thus, a two-dimensional secondaryelectron image generated by the electron beam applied to the wafersurface is formed at the field aperture position by the electrostaticlens (CL) and the intermediate lens (TL), which correspond to anprojector, and projected as a magnified image by the projection lens(PL). This image-forming optical system is called “secondary electronoptical system”.

It is preferable that a minus bias voltage (decelerating field voltage)should be applied to the wafer. The decelerating electric field has theeffect of decelerating the incident (irradiation) beam, which minimizesthe damage to the sample. In addition, the decelerating electric fieldaccelerates secondary electrons emitted from the sample surface by theelectric potential difference between the electrostatic lens (CL) andthe wafer, thereby effectively reducing chromatic aberration. Theelectrons converged by the electrostatic lens (CL) are focused throughthe intermediate lens (TL) to form a secondary electron image at thefield aperture (FA). The image is projected as a magnified image on themicrochannel plate (MCP) through the projection lens (PL). In thisoptical system, a numerical aperture NA is provided between theelectrostatic lens CL and the intermediate lens TL. The numericalaperture NA is optimized to form an optical system capable of minimizingoff-axis aberrations.

Further, an electrostatic octapole stigmator (STIG) is provided tocorrect errors in the manufacture of the electron optical systems andthe astigmatism and anisotropic aberration of magnification introducedinto the image by passing through the E×B filter (Wien filter).Misalignment is corrected by using a deflector (OP) disposed betweeneach pair of adjacent lenses. Thus, it is possible to attain an imageprojection optical system providing a uniform resolution in the field ofview.

The E×B deflector is a unit of an electromagnetic prism optical systemin which electrodes and magnetic poles are disposed in orthogonaldirections so that an electric field and a magnetic field intersect eachother at right angles. The E×B deflector can produce conditions (Wienconditions) under which when an electromagnetic field is selectivelyapplied to the field, an electron beam entering the field from onedirection is deflected, whereas an electron beam entering the field fromthe opposite direction is allowed to travel straight owing to the factthat the influence of force applied to the electron beam from theelectric field and the influence of force applied thereto from themagnetic field cancel each other. Thus, the primary electron beam isdeflected to be irradiated perpendicularly or normally to the wafersurface, while the secondary electron beam is allowed to travel straighttoward the detector.

The secondary electron image from the wafer formed by the secondaryelectron optical system is first amplified by the microchannel plate(MCP) and then converted into a light image through the fluorescentscreen. The principle of the MCP is as follows. A bundle of severalmillions of extremely short electrically conductive glass capillarieshaving a diameter of 6 to 25 μm and a length of 0.24 to 1.0 mm is shapedinto a thin plate. When a predetermined voltage is applied to the plate,each capillary operates as an independent secondary electron multiplier.Thus, the microchannel plate forms a secondary electron amplifier as awhole.

The light image produced through conversion by the fluorescent screen isprojected onto the TDI-CCD as a 1× magnified image by a relay opticalsystem placed in the atmospheric air through a vacuum transmissionwindow or by a relay optical system also serving as a vacuum feedthroughoptical system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the general arrangement of an imageprojection type electron beam inspection system according to anembodiment of the present invention.

FIG. 2 is a horizontal sectional view showing the detailed arrangementof an E×B deflector (i.e. an electron beam separator) in the electronbeam inspection system.

FIG. 3 is a sectional view showing a vertical sectional structure takenalong the line A—A in FIG. 2.

FIG. 4 is a diagram showing the general arrangement of an imageprojection type electron beam inspection system designed to apply aplurality of primary electron beams to an observation region of a samplesurface while the region being two-dimensionally scanned with theelectron beams.

FIG. 5 is a diagram for describing a method of irradiating primaryelectron beams in the system shown in FIG. 4.

FIG. 6 is a diagram schematically showing the arrangement of an electronbeam inspection system according to another embodiment of the presentinvention.

FIG. 7 is a block diagram showing in more detail a controller of theelectron beam inspection system shown in FIG. 6.

FIG. 8 is a diagram showing a wafer inspection procedure.

FIG. 9 is a diagram showing the array of pixels of a line sensor.

FIG. 10 is a diagram showing the arrangement of an image projection typeelectron beam inspection system according to the related art.

FIG. 11 is a diagram showing the arrangement of an image projection typeelectron beam inspection system according to still another embodiment ofthe present invention.

FIG. 12 is a diagram schematically showing an image projection typeelectron beam inspection system according to a further embodiment of thepresent invention.

FIGS. 13(A) and 13(B) are diagrams illustrating the operating principleof a magnetic lens shown in FIG. 12.

FIG. 14 is a diagram showing an example of placement of the magneticlens shown in FIG. 12.

FIG. 15 is a diagram showing another example of placement of themagnetic lens shown in FIG. 12.

FIG. 16 is a diagram schematically showing the arrangement of anelectron beam inspection system according to a further embodiment of thepresent invention.

FIG. 17 is a diagram showing the layout of a multiple optical column asa modification of the single optical column of the electron beaminspection system shown in FIG. 16.

FIG. 18 is a graph showing an axial potential distribution when avoltage is applied to each of electrodes and a sample.

FIG. 19 is a diagram showing an embodiment of a differential pumpingstructure provided in a charged particle beam inspection system as anelectron beam inspection system according to the present invention.

FIG. 20 is a diagram showing a modification of the differential pumpingstructure in which a high-purity inert gas outlet is directed toward theouter peripheral side.

FIG. 21 is a diagram showing another modification of the differentialpumping structure in which a vacuum chamber is provided in thedifferential pumping structure.

FIG. 22( a) is a diagram showing another modification of thedifferential pumping structure in which a member for height adjustmentis provided on a stage, the diagram illustrating a state where theoptical column is positioned in the vicinity of one end of the stage.

FIG. 22( b) is a diagram illustrating the modification shown in FIG. 22(a), the diagram showing a state where the optical column is positionedin the vicinity of the other end of the stage.

FIG. 23 is a diagram showing a modification of the charged particle beamsystem according to the present invention in which a height-adjustingmechanism is provided on the stage.

FIG. 24 is a diagram showing another modification of the differentialpumping structure in which the movable range of a sample moved by thestage is covered with a container filled with an inert gas.

FIG. 25 is a diagram showing another modification of the differentialpumping structure in which the whole movable range of the stage iscovered with a container filled with an inert gas.

FIG. 26 is a diagram showing another modification of the differentialpumping structure in which a vacuum chamber is communicably connected toa container filled with an inert gas.

FIG. 27 is a diagram showing another modification of the differentialpumping structure, the diagram illustrating an embodiment of anevacuation path.

FIG. 28 is a diagram showing another modification of the differentialpumping structure, the diagram illustrating a modification of theevacuation path.

FIG. 29 is a diagram showing another modification of the differentialpumping structure, the diagram illustrating an inert gas circulatingpath.

FIG. 30 is a diagram showing an arrangement in which a charged particlebeam system according to another embodiment of the present invention isapplied to a wafer defect inspection system.

FIG. 31 is a flowchart showing an embodiment of a semiconductor devicefabrication method according to the present invention.

FIG. 32 is a flowchart showing a lithography step, which is at the coreof a wafer processing step in FIG. 31.

FIG. 33 is a flowchart showing an inspection procedure according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An image projection type electron beam inspection system according to anembodiment of the present invention will be described below specificallyto clarify the relationship between the principal functions of the imageprojection system and the overall structure thereof.

FIG. 1 is a general view of the image projection type electron beaminspection system according to this embodiment. It should be noted,however, that part of the arrangement is omitted in the illustration.

In FIG. 1, the electron beam inspection system has a primary column 1, asecondary column 2, and a chamber 3. An electron gun 4 is provided inthe primary column 1. A primary optical system 5 is disposed on theoptical axis of an electron beam (primary beam) emitted from theelectron gun 4. A stage 6 is installed in the chamber 3. A sample W isplaced on the stage 6.

Meanwhile, the secondary column 2 contains a cathode lens 8, a numericalaperture 9, a Wien filter 10, a second lens 11, a field aperture 12, athird lens 13, a fourth lens 14, and a detector 15, which are disposedon the optical axis of a secondary beam generated from the sample W. Itshould be noted that the numerical aperture 9 corresponds to an aperturestop, which is a thin plate of a metal (e.g. Mo) with a circular hole.The numerical aperture 9 is disposed so that the aperture portionthereof is coincident with the position where the primary beam isfocused and also coincident with the focus position of the cathode lens8. Accordingly, the cathode lens 8 and the numerical aperture 29constitute a telecentric electron optical system.

Meanwhile, the output of the detector 15 is input to a control unit 16.The output of the control unit 16 is input to a CPU 17. Control signalsfrom the CPU 17 are input to a primary column controlling unit 18, asecondary column controlling unit 19 and a stage driving mechanism 7.The primary column controlling unit 18 controls the voltage applied tothe lenses of the primary optical system 5. The secondary columncontrolling unit 19 controls the voltage applied to each of the cathodelens 8 and the second to fourth lenses 11 to 14 and also controls theelectromagnetic field applied to the Wien filter 10.

The stage driving mechanism 7 transmits stage position information tothe CPU 17. The primary column 18, the secondary column 19 and thechamber 3 are connected to an evacuation system (not shown) andevacuated by a turbo molecular pump or the like of the evacuation systemso that the inside of each of them is kept under vacuum conditions.

The primary beam from the electron gun 4 enters the Wien filter 10 whilebeing subjected to the lens action of the primary optical system 5. Inthis embodiment, the tip of the electron gun 4 is a rectangular cathodeformed from LaB₆, which allows a large electric current to be obtained.The primary optical system 5 uses rotationally asymmetric quadrupole oroctopole electrostatic (or electromagnetic) lenses, which can causeconvergence and divergence along each of the X- and Y-axes. Such lensesare arranged in two or three stages. By optimizing the conditions ofeach lens, the beam irradiation region on the sample surface can beshaped into any desired rectangular or elliptical configuration withoutloss of the incident electrons.

More specifically, when an electrostatic lens is used, four columnarrods (quadrupole) are used. Mutually opposing electrodes are placed inan equipotential state and given voltage characteristics opposite toeach other.

It should be noted that the quadrupole lens is not necessarily limitedto the column-shaped lens but may be a lens having a configurationdefined by dividing a circular plate into four parts, which is generallyused in an electrostatic deflector. In this case, it is possible toreduce the size of the lens. The primary beam passing through theprimary optical system 5 is bent by the deflecting action of the Wienfilter 10. The Wien filter 10 has a magnetic field and an electric fieldarranged to intersect each other at right angles and allows only chargedparticles satisfying the Wien condition E=vB to travel straight. In theWien condition E=vB, E is the electric field, B is the magnetic field,and v is the velocity of the charged particles. The Wien filter 10 bendsthe path of the other charged particles. For the primary beam, force FBdue to the magnetic field and force FE due to the electric field act tobend the beam path. For the secondary beam, the force FB and the forceFE act in the opposite directions and hence cancel each other.Accordingly, the secondary beam travels straight as it is.

The lens voltage for the primary optical system 5 is preset so that aelectron beam crossover is focussed at the aperture portion of thenumerical aperture 9. In other words, Koehler illumination used inoptical microscopes is realized. The numerical aperture 9 eliminates anelectron beam undesirably scattered in the system from reaching thesample surface, thereby preventing charge-up and contamination of thesample W.

When the primary beam is irradiated to the sample W, secondaryelectrons, reflected electrons or back-scattered electrons are emittedas a secondary beam from the beam-irradiated surface of the sample W.

The secondary beam passes through the cathode lens 8 while beingsubjected to the lens action thereof.

Incidentally, the cathode lens 8 comprises three electrodes. Thelowermost electrode is designed to form a positive electric field withrespect to the sample W so that the secondary electrons are efficientlydrawn into the cathode lens 8.

The lens action is produced by applying a voltage to the first andsecond electrodes of the cathode lens 8 and placing the third electrodeat zero potential. Meanwhile, the numerical aperture 9 is placed at thefocus position of the cathode lens 8, that is, at the back focusposition from the sample W. Accordingly, a beam of electrons emittedfrom positions off the field center (i.e. off-axis points) is alsoformed into a parallel beam and passes through the center of thenumerical aperture 9 without being eclipsed.

It should be noted that the numerical aperture 9 also serves to suppresslens aberrations introduced into the secondary beam from the second tofourth lenses 11 to 14. The secondary beam passing through the numericalaperture 9 travels straight through the Wien filter 10 without beingsubjected to the deflecting action of the Wien filter 10.

If the secondary beam is focused to form an image by the cathode lens 8alone, chromatic aberration of magnification and distortion are likelyto occur. Therefore, the cathode lens 8 is combined with the second lens11 to perform first image formation. The secondary beam forms anintermediate image at the field aperture 12 through the cathode lens 8and the second lens 11. In this case, it is generally likely that themagnifying power necessary for the secondary optical system will becomeinsufficient. Therefore, the third lens 13 and the fourth lens 14 areadded to magnify the intermediate image. The third and fourth lenses 13and 14 are arranged so that a magnifying image-forming operation takesplace when the secondary beam passes through each of the third andfourth lenses 13 and 14. That is, a total of three image-formingoperations take place in this optical system. It should be noted thatthe third lens 13 and the fourth lens 14 may be arranged to perform oneimage-forming operation in combination (i.e. a total of twoimage-forming operations take place in the optical system).

The second to fourth lenses 11 to 14 are all rotationally symmetriclenses (or lenses symmetric with respect to the optical axis) known as“unipotential lenses” or “Einzel lenses”. Each lens comprises threeelectrodes. Normally, two outer electrodes are placed at zero potential,and a voltage is applied to the central electrode to effect lens actionunder control. The field aperture 12 is disposed at a point where theintermediate image is formed. The field aperture 12 limits the visualfield to a necessary range as in the case of the field stop of anoptical microscope. The field aperture 12 also serves to eliminate anunnecessary electron beam in cooperation with the third lens 13 and thefourth lens 14 provided in the subsequent stage, thereby preventing thegeneration of noise in the detector 15 and contamination thereof. Itshould be noted that the magnifying factor is set by varying the lensconditions (focal length) of the third and fourth lenses 13 and 14.

The secondary beam is projected by the secondary optical system to forma magnified image on the detecting surface of the detector 15. Thedetector 15 includes a microchannel plate (MCP) for multiplyingelectrons and a fluorescent screen for converting the electrons intolight. The detector 15 further includes a lens and other optical systemfor relaying and transmitting the optical image from the vacuum systemto the outside, together with an image pickup device (e.g. a CCD). Thesecondary beam is focused onto the MCP detecting surface and multipliedby the MCP. The multiplied electrons are converted into a light signalby the fluorescent screen and then converted into a photoelectric signalby the image pickup device.

The control unit 16 reads the sample image signal from the detector 15and transmits it to the CPU 17. The CPU 17 inspects the pattern on thesample W for defects on the basis of the image signal by templatematching or the like. The stage 6 is movable in the X- and Y-directionsby the stage driving mechanism 7. The CPU 17 reads the position of thestage 6 and outputs a drive control signal to the stage drivingmechanism 7 to drive the stage 6, thereby sequentially performing thedetection and inspection of the image are carried out.

Regarding the secondary beam, all the principal rays from the sample Ware incident perpendicularly or normally on the cathode lens 8 (i.e. inparallel to the optical axis of the lens 8) to pass through thenumerical aperture 9. Therefore, marginal rays of light are noteclipsed. Hence, there is no reduction in the image luminance at theperipheral portion of the sample W. Usually, variations in the electronenergy cause the image formation position to differ. That is, chromaticaberration of magnification (chromatic difference of magnification)occurs (in particular, the secondary electrons suffer large chromaticaberration of magnification because of large variations in energy).However, the chromatic aberration of magnification can be suppressed byplacing the numerical aperture 9 at the focus position of the cathodelens 8.

Because the change of the magnifying power is made after the secondaryelectrons have passed through the numerical aperture 9, even if themagnifications of the third and fourth lenses 13 and 14, which have beenset as lens conditions, are varied, it is possible to obtain a uniformimage over the whole field of view on the detector side. Although avariation-free, uniform image can obtained in this embodiment, when themagnifying factor is raised, usually, the brightness of the image lowersunfavorably. To solve this problem, the lens conditions of the primaryoptical system are set so that when the magnifying factor is changed byvarying the lens conditions of the secondary optical system, theeffective visual field on the sample surface, which is determined by themagnifying power, and the electron beam irradiated to the sample surfacehave the same size.

More specifically, as the magnification is raised, the visual fieldbecomes narrower. However, if the electron beam irradiation energydensity is increased at the same time as the magnification is raised,the detected electron signal density is kept constant at all times evenif the secondary electrons are projected as a magnified image by thesecondary optical system. Thus, the brightness of the image will notlower.

Although the electron beam inspection system in this embodiment uses theWien filter 10 that bends the path of the primary beam but allows thesecondary beam to travel straight, the present invention is notnecessarily limited to the described arrangement. The electron beaminspection system may use a Wien filter that allows the primary beam totravel straight but bends the path of the secondary beam. Further, inthe foregoing embodiment, a rectangular beam is formed by using arectangular cathode and a quadrupole lens system. However, the presentinvention is not necessarily limited to the described arrangement. Forexample, a rectangular beam or an elliptical beam may be produced from acircular beam. Alternatively, a rectangular beam may be formed bypassing a circular beam through a slit.

The structure of the electron beam deflector 10 operating as a Wienfilter, i.e. an E×B deflector, will be described below in detail withreference to FIG. 2 and FIG. 3, which shows a vertical section takenalong the line A—A in FIG. 2. As shown in FIG. 2, the field of theelectron beam deflector 10 has a structure in which an electric fieldand a magnetic field are placed to intersect each other at right anglesin a plane perpendicular to the optical axis of an image projectionoptical part (i.e. a part in which a one- or two-dimensional image ofsecondary electrons and reflected electrons emitted according to theconditions of the sample surface when an electron beam is applied to thesample is formed on the electron beam detector). That is, the electronbeam deflector 10 has an E×B structure.

In the electron beam deflector 10, the electric field is generated byelectrodes 10-1 and 10-2 each having a concavely curved surface. Theelectric field generated by the electrodes 10-1 and 10-2 is controlledby control units 10 a and 10 d. Meanwhile, electromagnetic coils 10-1 aand 10-2 a are disposed to face each other in a direction perpendicularto the direction in which the electric field-generating electrodes 10-1and 10-2 face each other, thereby generating a magnetic field. It shouldbe noted that the electric field-generating electrodes 10-1 and 10-2 arein point symmetry (the electrodes 10-1 and 102 may be in concentricrelation to each other).

In this case, in order to improve the uniformity of the magnetic field,pole pieces having a plane-parallel plate configuration are provided toform a magnetic path. The behavior of the electron beam in the verticalsection taken along the line A—A is as shown in FIG. 3. The incidentelectron beam 1 a is deflected by the electric field generated by theelectrodes 10-1 and 10-2 and the magnetic field generated by theelectromagnetic coils 10-1 a and 10-2 a. Thereafter, the electron beam 1a is incident on the sample surface in a direction perpendicularthereto.

The position through which the incident electron beam 1 a enters theelectron beam deflector 10 and the incident angle of the electron beam 1a are uniquely determined when the electron energy is determined.Further, the electric field generated by the electrodes 10-1 and 10-2and the magnetic field generated by the electromagnetic coils 10-1 a and10-2 a are controlled by the control units 10 a and 10 d and the controlunits 10 c and 10 b, respectively, so as to satisfy the condition forthe electric and magnetic fields, i.e. vB=E, so that secondary electrons2 a travel straight. Consequently, the secondary electrons 2 a travelstraight through the electron beam deflector 10 to enter the imageprojection optical part. In the above condition vB=E, v is the velocity(m/s) of the electrons 2 a, B is the magnetic field (T), and E is theelectric field (V/m).

Next, another embodiment of the defect inspection system utilizing theimage projection system will be described.

The defect inspection system utilizing the image projection systeminvolves the following problems: {circle around (1)} because an electronbeam is applied to the whole observation region of the sample surface byone shot, charge-up is likely to occur on the sample surface; and{circle around (2)} there is a limit to the electron beam currentobtained by this system (about 1.6 μA), which is an obstacle toimprovement in the inspection speed.

In this embodiment, a plurality of primary electron beams are used, andthe primary electron beams are applied to an observation region on thesample surface while the observation region is scanned with the primaryelectron beams two-dimensionally (X- and Y-directions; i.e. whileperforming raster scanning). Further, the image projection system isadopted for the secondary electron optical system. With thisarrangement, the above-described problems can be solved. The defectinspection system according to this embodiment has the above-describedadvantages of the image projection system. In addition, scanning with aplurality of primary electron beams makes it possible to solve theproblems of the image projection system: {circle around (1)} because anelectron beam is applied to the whole observation region of the samplesurface by one shot, charge-up is likely to occur on the sample surface;and {circle around (2)} there is a limit to the electron beam currentobtained by this system (about 1.6 μA), which is an obstacle toimprovement in the inspection speed. That is, because the electron beamirradiation point moves, it is easy for the electric charge to escape.Consequently, charge-up reduces. The required electric current value canbe readily increased by increasing the number of electron beams used. Inthis embodiment, when four primary electron beams are used, for example,if the electric current of one electron beam is 500 nA (electron beamdiameter: 10 μm), an electric current of 2 μA is obtained in total. Thenumber of primary electron beams can readily be increased to about 16electron beams. In this case, 8 μA can be obtained in theory. To scan asample with a plurality of primary electron beams, not only theabove-described raster scanning but also other types of scanning, e.g.Lissajous's figure scanning, can be used as long as the plurality ofprimary electron beams can be applied so that the amount of irradiationwith the electron beams is uniform throughout the irradiated region.Accordingly, the directing direction of the stage for scanning is notnecessarily limited to the direction perpendicular to the directingdirection of the plurality of electron beams for scanning.

As an electron beam source in this embodiment, it is possible to use athermal electron beam source (in which electrons are emitted by heatingan emissive material). In this case also, it is preferable to use LaB₆as an emissive (emitter) material. Other materials are also usable,provided that they have a high melting point (the vapor pressure at hightemperatures is low) and a low work function. To obtain a plurality ofelectron beams, two methods are available. One is a method wherein asingle electron beam is obtained from a single emitter (with a singleprojection) and passed through a thin plate (aperture plate) providedwith a plurality of holes, thereby obtaining a plurality of primaryelectron beams. The other is a method wherein a plurality of primaryelectron beams are drawn out directly from a plurality of tips formed ona single cathode material. Either of the methods makes use of theproperty of the electron beam that it is readily emitted from the tip ofa projection. It is also possible to use other types of electron beamsources, e.g. a thermal electric field emission type electron beamsource. The thermal electric field emission type electron beam source isa system in which electrons are emitted by applying a high electricfield to an emissive material, and the emission of electrons isstabilized by heating its electron beam emitting part.

Next, the above-described embodiment, in which a plurality of primaryelectron beams are irradiated to an observation region on the samplesurface while the region is scanned with the electron beamtwo-dimensionally (X- and Y-directions; i.e. while performingraster-scanning), and the image projection system is adopted for thesecondary electron optical system, will be described in more detail withreference to FIGS. 4 and 5.

In the following embodiment, a method wherein a plurality of primaryelectron beams are drawn out directly from a plurality of tips formed ona single emitter is adopted as a method of obtaining a plurality ofprimary electron beams.

As shown in FIG. 4, four electron beams 21 (21-1, 21-2, 21-3 and 21-4)emitted from an electron gun 20 are shaped by an aperture 50-1 andpassed through lenses 22-1 and 22-2 arranged in two stages to form anelliptical image having a size of 10 μm by 12 μm on the deflectioncenter plane of a Wien filter 23. Raster-scanning is performed by adeflector 26 in a direction perpendicular to the plane of the figure sothat the four electron beams is formed into an image so as to uniformlycover a rectangular region of 1 mm by 0.25 mm as a whole. The electronbeams deflected by the E×B deflector 23 serving as a Wien filter form acrossover at the numerical aperture NA. The beams thus formed arereduced to ⅕ by a lens 24 and projected onto the surface of a sample Wso as to cover a region of 200 μM by 50 μm and be appliedperpendicularly or normally to the sample surface. Consequently, foursecondary electron beams 25 carrying pattern image (sample image F)information are emitted from the sample W. The electron beams 25 aremagnified through the lenses 24, 27-1 and 27-2 and focused onto an MCP28-1 as a rectangular image (magnified projected image F′) composed ofthe four electron beams 25. The magnified projected image F′ formed fromthe secondary electron beams 25 is intensified 10,000 times by the MCP28-1 and converted into light by a fluorescent part 28-2. The light thusobtained is converted into an electric signal synchronized with thecontinuously moving speed of the sample W by a TDI (Time DelayIntegration)-CCD 29. The electric signal is acquired as a continuousimage by an image display unit 30 and output onto a CRT or the like.

The electron beam irradiation unit needs to irradiate the sample surfacewith the electron beam in a rectangular configuration as uniformly aspossible and with minimized variations of irradiation. In order toincrease throughput, it is necessary to apply the electron beam to theregion to be irradiated with an increased electric current. Conventionalsystems suffer electron beam irradiation variations of the order of ±10%and hence large image contrast variations. Further, in the conventionalsystems, the electron beam current is as small as about 500 nA at theirradiated region. Therefore, high throughput cannot be obtained. Inaddition, because in this type of system a wide image observation regionis entirely irradiated with an electron beam by one shot, an imagingtrouble due to charge-up is more likely to occur than in the case of thescanning electron microscope (SEM) system.

The primary electron beam irradiation method according to thisembodiment is shown in FIG. 5. The combination of electron beams 21consists of four electron beams 21-1, 21-2, 21-3 and 21-4. Each beam hasan elliptical sectional configuration with a size of 2 μm by 2.4 μm anda rectangular region of 200 μm by 12.5 μm is raster-scanned with eachbeam in such a manner that the raster-scanned regions do not overlapeach other. Thus, a rectangular region of 200 μm by 50 μm as a whole isirradiated with the four electron beams 21-1, 21-2, 21-3 and 21-4. Thebeam at a point 21-1 arrives at 21-1′ in a finite time and then returnsto a point directly below 21-1 (toward 21-2), which is away from 21-1 bya distance corresponding to the beam spot diameter (10 μm), withsubstantially no loss of time. Then, the beam moves parallel to the path21-1 to 21-1′, to a point directly below 21-1′ (toward 21-2′) again inthe same finite time as the above. This is repeated to scan ¼ (200 μm by12.5 μm) of the rectangular irradiation region indicated by the dottedline in the figure. Thereafter, the beam returns to the starting point21-1. This operation is repeated at high speed. The other electron beams21-2 to 21-4 repeatedly are directed for scanning in the same way and atthe same speed as the electron beam 21-1, thereby uniformly speedilyirradiating the rectangular irradiation region (200 μm by 50 μm) shownin the figure as a whole. The scanning method is not necessarily limitedto the above-described raster scan but may be other types of scanning,provided that the irradiation region can be irradiated uniformly. Forexample, the beam scan may be performed in such a manner as to draw aLissajous's figure. Therefore, the stage moving direction is notnecessarily limited to the direction A shown in the figure. That is, thestage moving direction does not always need to be perpendicular to thescanning direction (the high-speed scanning direction, i.e. thehorizontal direction in the figure). According to this embodiment,electron beam irradiation variations were favorably reduced to about±3%. The irradiation electric current was 250 nA per electron beam. Atthe sample surface, the four electron beams provided 1.0 μA as a whole(double the value obtained with the conventional system). Thus, anincrease in the number of electron beams applied makes it possible toincrease the electric current and to obtain increased throughput. Inaddition, the irradiation point is smaller than in the conventionalsystem (about 1/80 in terms of area) and moving. Therefore, it waspossible to suppress charge-up to 1/20 or less of that in theconventional system.

Although not shown in the figure, the system according to thisembodiment has, in addition to the lenses, a limiting field aperture(selector aperture), a deflector (aligner) having four or more electrodefor alignment of electron beams, an astigmatism corrector (stigmator),and units necessary for electron beam illumination and image formation,such as a plurality of quadrupole lenses (four-pole lenses) for shapingthe beams.

Next, another embodiment of the image projection type electron beaminspection system will be described. The electron beam inspection systemaccording to this embodiment is designed so that defect inspection of asample (e.g. a wafer or a mask), particularly a wafer having a devicepattern with a minimum line width of 0.1 μm or less, can be performedwith high throughput and high reliability.

First, the outline of this embodiment will be described.

The image projection type electron beam inspection system according tothis embodiment shapes an electron beam emitted from an electron guninto a rectangular electron beam, applies the electron beam to thesurface of a wafer, and directs secondary electrons emitted from thewafer surface toward a detector to form a secondary electron image. Suchan image projection type electron beam inspection system for defectinspection uses a rectangular or planar beam having a diameter largerthan the beam spot diameter in scanning electron microscopes, and imagesthe whole irradiated region by one shot to acquire an image thereof.Accordingly, the image projection type electron beam inspection systemcan provide higher throughput than in the case of the scanning type.Thus, it is possible to meet the demand for higher throughput. Further,with this system, the whole wafer surface is scanned with an electronbeam by moving the stage continuously. Secondary electrons emitted fromthe wafer as a result of the scanning are converted into an opticalimage through a fluorescent screen, and the image thus obtained isdetected with a line sensor (TDI-CCD).

In such a line sensor, as shown in FIG. 9, n CCD pixels C₁ to C_(n) arearranged in a line in the direction (horizontal direction in the figure)of one of two orthogonal axes to form one CCD pixel row, and m CCD pixelrows ROW-1 to ROW-m are arranged in the other axis direction (verticaldirection in the figure) to form a CCD array. Electric chargesaccumulated in each CCD pixel row are transferred simultaneously in thevertical direction by a distance corresponding to one CCD pixel inresponse to one vertical clock signal given externally (i.e. theelectric charges move in the direction of the arrows E). A line image ofn pixels picked up in ROW-1 at a certain time is transferred to ROW-2when a clock signal is given. When a subsequent clock signal is given,the line image transferred to ROW-2 further moves vertically by adistance corresponding to one pixel, thereby being transferred to ROW-3.In this way, charge transfer is repeatedly performed up to ROW-m as theimage moves. Finally, the electric charges are taken out of the linesensor from a horizontal output register as image data.

However, if the charge transfer time (hereinafter referred to as “linerate”) of the lines sensor is kept constant during the imagingoperation, image blur may be caused by asynchronous charge transfer inthe line sensor owing to variations in the stage moving speed, whichgives rise to no problem in the defect inspection system utilizing thescanning electron microscope system. In addition, when there is a changein the magnification of the electron optical system caused by thefocusing mechanism due to the inspection of the whole surface of thewafer, the pixel size on the wafer changes. This causes the optimum linerate to vary, resulting in image blur similar to the above.

An object of this embodiment is to provide an electron beam inspectionsystem for defect inspection that is capable of avoiding image blur ascaused by asynchronous charge transfer by making the line rate of theline sensor synchronous with the stage moving speed at all times.

Another object of this embodiment is to provide an electron beaminspection system for defect inspection that is capable of avoidingimage blur as caused by a change in the magnification of the electronoptical system.

Accordingly, the image projection type electron beam inspection systemfor defect inspection according to this embodiment has a primaryelectron optical system for shaping an electron beam emitted from anelectron gun into a desired configuration and for irradiating the shapedelectron beam to a surface of a sample to be inspected. A secondaryelectron optical system forms an image of secondary electrons emittedfrom the sample. A detector converts the formed secondary electron imageinto an optical image through a fluorescent screen and detects theoptical image with a line sensor. The electron beam inspection system isprovided with a controller whereby the charge transfer time at which apicked-up line image is transferred between each pair of adjacent pixelrows provided in the line sensor is controlled in association with themoving speed of a stage for moving the sample. The stage moving speed isdetected, and an optimum line rate is calculated and fed back, wherebythe line rate of the line sensor is synchronized with the stage movingspeed at all times. Thus, image blur as caused by asynchronous chargetransfer can be avoided.

In a modification of the electron beam inspection system according tothis embodiment, the charge transfer time of the line sensor iscontrolled in association with a change of the magnification of theprimary and secondary electron optical systems. Thus, even when there isa change in the magnification of the electron optical systems caused bythe focusing mechanism due to the inspection of the whole surface of thewafer, image blur as caused by asynchronous charge transfer can beavoided.

In another modification, a microchannel plate is placed in the stagepreceding the fluorescent screen to multiply the secondary electrons inthe secondary electron optical system.

In another modification, the electron beam inspection system has a laserinterferometer for measuring the position of the stage. Thus, stageposition information can be detected from the laser interferometer, andan optimum line rate can be calculated from the stage moving speed andfed back. Accordingly, it is possible to synchronize the line rate ofthe line sensor with the stage moving speed at all times and hencepossible to avoid image blur as caused by asynchronous charge transfer.

The image projection type electron beam inspection system for defectinspection according to this embodiment will be described below morespecifically with reference to the accompanying drawings.

FIG. 6 shows schematically an electron beam inspection system 1001 fordefect inspection according to this embodiment. The electron beaminspection system 1001 for defect inspection has a primary electronoptical system 1002 for shaping an electron beam emitted from anelectron gun into a desired configuration (e.g. a rectangular orelliptical shape) and for irradiating the shaped electron beam to asurface of a sample (e.g. a wafer or a mask; referred to as “wafer” inthis embodiment) S to be inspected. The electron beam inspection system1001 also has a secondary electron optical system 1003. The secondaryelectron optical system 1003 magnifies and projects secondary electronsemitted from the wafer S onto a detector 1004. The electron beaminspection system 1001 also has the detector 1004. The detector 1004converts the secondary electrons into an image of light and furtherconverts it into an electric signal. The electron beam inspection system1001 further has a controller 1005 (see FIG. 7) for controlling thedetector 1004.

The primary electron optical system 1002 has an electron gun 1022 foremitting an electron beam 1021 and a primary system electrostatic lensunit 1023 for shaping the electron beam 1021 into a beam with apredetermined sectional configuration. As shown in FIG. 6, theconstituent elements of the primary electron optical system 1002 arearranged in series at a predetermined angle to a direction perpendicularto the surface of the wafer S, with the electron gun 1022 placed at theuppermost position. The primary electron optical system 1002 further hasan E×B separator 1024 for deflecting the electron beam 1021 andseparating secondary electrons emitted from the wafer S by a field inwhich an electric field and a magnetic field intersect each other atright angles. Further, the primary electron optical system 1002 has anelectrostatic objective lens 1025. The E×B separator 1024 and theelectrostatic objective lens 1025 are arranged in series in a directionperpendicular to the surface of the wafer S.

The secondary electron optical system 1003 is arranged in the directionperpendicular to the surface of the wafer S along an optical axis A ofsecondary electrons 1031 from the wafer S separated by the E×B separator1024 and has a secondary system electrostatic lens unit 1032 to magnifyand project the secondary electrons 1031.

The detector 1004 has an MCP (Micro-Channel Plate) 1041, a fluorescentscreen 1042 for converting the secondary electrons 1031 from thesecondary electron optical system 1003 into a light image, a line sensor1043 for detecting the light image, a memory 1044 for storing waferimage information detected by the line sensor 1043, and a CRT monitor1045 for displaying the wafer image.

As shown in FIG. 7, the controller 1005 has a laser interferometer 1051for measuring the position of the stage, an A/D converter 1052 forconverting the position signal from the laser interferometer 1051, aline rate control unit 1053 for computing an optimum line rate on thebasis of the position signal from the laser interferometer 1051 andoutputs the optimum line rate, a D/A converter 1054 for converting theoutput signal from the line rate control unit 1053, and a line sensorcontrol unit 1055 for controlling the line sensor 1043 on the basis ofthe signal from the line rate control unit 1053.

The above-described constituent elements may be those publicly known. Adetailed description of the structures thereof is omitted.

In the electron beam inspection system 100 arranged as stated above,electrons emitted from the electron gun 1022 are accelerated and shapedinto an electron beam 1021 having a rectangular or elliptical sectionalconfiguration through the primary system electrostatic lens unit 1023.The shaped electron beam 1021 forms a rectangular or elliptical image ata position slightly above the deflection principal plane of the E×Bseparator 1024. The electron beam image entering the E×B separator 1024is deflected therein to a direction perpendicular to the surface of thewafer S and irradiated to the surface of the wafer S after beingdemagnified and decelerated by the electrostatic objective lens 1025.

Secondary electrons 1031 emitted from the wafer S by the electron beamirradiation are converged by the electrostatic objective lens 1025 toenter the E×B separator 1024. The secondary electron beam directedtoward the secondary electrostatic lens system 1032 by the E×B separator1024 passes through the secondary electrostatic lens system 1032 and isprojected onto the MCP 1041 as a magnified image.

The secondary electrons 1031 entering the MCP 1041 are multipliedtherein and are irradiated to the fluorescent screen 1042. The secondaryelectrons 1031 irradiated to the fluorescent screen 1042 are convertedinto a light image. The image is detected and converted into an electricsignal by the line sensor 1043. Wafer image data converted into anelectric signal is transmitted through an optical fiber cable to thememory 1044 of a personal computer where it is stored as wafer imageinformation. The wafer image information is displayed on the CRT monitor1045 to detect a possible defect.

Next, the operation of the controller 1005 will be described withreference to FIGS. 6 and 7. A wafer S to be inspected is placed on anX-Y stage 1006. In a case where a wafer is inspected by a method such asthat described above, the X-Y stage 1006 is moved in the Y-direction atconstant speed. A line rate calculated from the X-Y stage driving speedand the pixel size on the wafer is set in the line sensor control unit1055 as a constant, and the image of the line sensor 1043 is displayedon the CRT monitor 1045. If the moving speed of the X-Y stage 1006 andthe line rate are not synchronized with each other, several fringepatterns appear synchronously with variations in speed of the X-Y stage1006 and perpendicularly to the stage scanning direction. This causesthe image to be blurred.

To solve the problem of image blur due to the fringe patterns, thecontroller 1005 performs the following control. The position of the X-Ystage 1006 during movement thereof is measured with the laserinterferometer 1051. The serial output signal from the laserinterferometer 1051 is converted into a digital signal in 16 bits at aclock frequency of 200 MHz by the A/D converter 1052, and present stageposition information Xt is output to the line rate control unit 1053. Inaddition, position information Xt-1 one cycle before the present cycle,together with a delay time, is input to the line rate control unit 1053.The line rate control unit 1053 calculates a speed component of the X-Ystage 1006 from these pieces of position information and the delay time.Further, the line rate control unit 1053 computes an optimum line ratefrom the stage speed component and the pixel size on the wafer andoutputs a signal indicating information thus obtained. The output signalis converted into an analog signal in 16 bits at a clock frequency of200 MHz by the D/A converter 1054. The analog signal is input to theline sensor control unit 1055. The line rate of the line sensor 1043 iscontrolled by the signal from the line sensor control unit 1055. Theline rate of the line sensor 1043 is updated by the command from theline sensor control unit 1055. Thus, the image blur can be avoided. Inthis case, the overall time delay in the controller 1005, including theinput and output operations, is sufficiently small relative to thevibration period of the X-Y stage 1006, which is well greater thanseveral microseconds.

An actual wafer inspection was performed by using the above-describedelectron beam inspection system according to this embodiment. In FIG. 8,first, the top left inspection starting point S2 in a wafer inspectionregion S1 of about 130 mm by 130 mm was moved to the center of a regionfor irradiation with the electron beam 1021. Thereafter, the X-Y stage1006 was moved in the +Y direction at 10 mm/sec. to inspect the wafer S.Consequently, the wafer inspection region S1 was inspected in thedirection of the arrow B. Next, the X-Y stage 1006 was moved in the −Xdirection to step by about 500 microns. Consequently, the waferinspection region S1 was shifted in the direction of the arrow C. Next,the X-Y stage 1006 was moved in the −Y direction to inspect the wafer S.In this case, the wafer inspection region S1 was inspected in thedirection of the arrow D. In this way, scanning was repeated to inspectthe whole wafer inspection region S1.

When scanning was performed by moving the X-Y stage 1006 from theinspection starting point S2 in the +Y direction at a stage speed of 10mm/sec., the stage speed varied cyclically, showing a deviation of theorder of ±10%, with a period of 2.5 milliseconds. In this case, the linerate having a frequency in the neighborhood of 300 kHz was cyclicallyoscillated synchronously with the stage speed variations by the linerate control unit 53, whereby a blur-free, favorable image was obtained.

When scanning was performed by moving the X-Y stage 1006 in the −Ydirection at a stage speed of 10 mm/sec., the stage speed showedvariations similar to those during the scanning in the +Y direction.However, by performing control similar to the above, a favorable imagewas obtained.

This embodiment provides the following advantages:

-   (1) An optimum line rate signal calculated in the line rate control    unit is fed back to the external input terminal of the line sensor    control unit for controlling the line rate of the line sensor,    whereby the line rate of the line sensor is synchronized with the    moving speed of the X-Y stage at all times. Accordingly, it is    possible to avoid image blur which would otherwise occur owing to    the charge transfer delay in the line sensor.-   (2) Even when there is a change in the magnification of the electron    optical system caused by the autofocusing mechanism due to the    inspection of the whole surface of the wafer, image blur as caused    by asynchronous charge transfer can be avoided by feeding back the    optimum line rate signal calculated in the line rate control unit to    the external input terminal of the line sensor control unit.-   (3) It is possible to actively control image blur caused by the line    sensor due to vibrations of the X-Y stage or variations in the speed    of the X-Y stage driving motor.

Next, another embodiment of the image projection type electron beaminspection system will be described. The electron beam inspection systemaccording to this embodiment relates to a multi-purpose electron beaminspection system.

First, a technique relating to the image projection type electron beaminspection system according to this embodiment will be described.

In general, the image projection type electron beam inspection systemhas a single electron beam irradiation unit. In this case, if anelectron beam is applied obliquely to the surface of a sample and anelectron beam is taken out from a direction perpendicular to the samplesurface, a shadow may be undesirably produced by the unevenness of thesample surface. Therefore, a Wien filter (E×B filter) is used, and theintensities of the electric and magnetic fields in the Wien filter areso set that the obliquely applied electron beam is deflected so as to beincident perpendicularly or normally on the sample surface, whereassecondary electrons from the sample are taken out in a directionperpendicular to the sample surface without being deflected.

FIG. 10 is a block diagram showing the arrangement of an imageprojection type electron beam inspection system 2034 according to therelated art. The electron beam inspection system 2034 has an electrongun 2001 for applying a primary electron beam 2102 to a sample 2110, adetector 2114 for detecting secondary electrons 2111 emitted from thesample surface by irradiation with the primary electron beam 2102 andgenerating an image signal, a Wien filter 2105 having electrodes 2106and magnets 2107, a first lens system 2003 and a second lens system 2004for shaping the primary electron beam 2102, a third lens system 2108 anda fourth lens system 2109 positioned between the Wien filter 2105 andthe sample 2110, and a sixth lens system 2112 and a seventh lens system2113 positioned between the Wien filter 2105 and the detector 2114. Inthe electron beam inspection system, the Wien filter 2105 is set so asto deflect the primary electron beam 2102 emitted from the electron gun2001 but allow the secondary electrons 2111 emitted from the samplesurface to travel straight. The Wien filter 2105 makes the primaryelectron beam 2102 incident perpendicularly or normally on the samplesurface. This type of system is disclosed, for example, in JapanesePatent Application Unexamined Publication (KOKAI) No. Hei 11-132975.

The above-described electron beam inspection system is a single-purposesystem. As the wafer size increases from 8 inches through 12 inches to15 inches, the floor area of the electron beam inspection system becomeslarger. Moreover, because of the need to perform various inspecting andmeasuring operations, the proportion of the floor area occupied by theelectron beam inspection system in the clean room of semiconductorproduction facilities increases unfavorably.

An object of this embodiment is to provide an electron beam inspectionsystem having a plurality of functions by itself, thereby allowingin-process wafers to be inspected with a reduced number of electron beaminspection systems. Another object of this embodiment is to provide anelectron beam inspection system having a plurality of functions, therebyreducing the proportion of the floor area occupied by the electron beaminspection system in the clean room of semiconductor productionfacilities. Other objects and advantages of this embodiment will becomeapparent from the following description.

Thus, the image projection type electron beam inspection system fordefect inspection according to this embodiment is a multi-purposeelectron beam inspection system for inspecting the condition of thesurface of a sample by irradiating a primary electron beam to the sampleand detecting secondary electrons emitted from the sample surface. Themulti-purpose electron beam inspection system has an electron source forgenerating a primary electron beam, a lens system for shaping theprimary electron beam, an optical system for directing the primaryelectron beam for scanning, a sample stage for supporting a sample, andan optical system for directing secondary electrons toward a detector,and the detector for detecting the secondary electrons to generate animage signal. The multi-purpose electron beam inspection system furtherhas at least two functions selected from among defect detection on thesample surface, defect review on the sample surface, pattern line widthmeasurement, and pattern electric potential measurement. The twofunctions may be the sample surface defect detection and the samplesurface defect review.

In the multi-purpose electron beam inspection system according to thisembodiment, the sample surface defect detection may be effected bycomparing an image obtained from the image signal with pattern data orby comparing the images of dice with each other. The sample surfacedefect review may be performed by observation of an image on a monitorobtained by beam scanning synchronized with the scanning of the primaryelectron beam over the wafer surface. The pattern line width measurementmay be made on the basis of a secondary electron image obtained when theprimary electron beam is directed for scanning over the wafer surface inthe direction of the short side of a pattern. The pattern electricpotential measurement may be carried out in such a manner that anegative electric potential is applied to the electrode closest to thesample surface, whereby secondary electrons emitted from a pattern onthe sample surface that has a high electric potential are selectivelydriven back toward the sample.

The multi-purpose electron beam inspection system according to thisembodiment inspects the condition of the surface of a sample by applyinga primary electron beam to the sample and detecting secondary electronsemitted from the sample surface. The multi-purpose electron beaminspection system has a lens system capable of shaping the primaryelectron beam into at least two configurations selected from amongrectangular, circular and spot-shaped configurations, a primary electronoptical system having a deflection system for moving the electron beamin a desired direction for scanning, and a detection system fordirecting secondary electrons emitted from the sample surface toward adetector. The multi-purpose electron beam inspection system has thefunction of automatically detecting a possible defect and the functionof outputting information concerning the position of a detected defectand further has the function of allowing observation of theconfiguration of the defect. The detection system may include an imageprojection optical system. Further, the detection system may include asecondary electron multiplier.

A plurality of multi-purpose electron beam inspection systems accordingto this embodiment may be combined together as follows. A group ofmulti-purpose electron beam inspection systems may be disposed in one ormore lines. The group of multi-purpose electron beam inspection systemsmay share a common sample stage and inspect a sample on the commonsample stage. Each of the multi-purpose electron beam inspection systemsmay be arranged to irradiate a plurality of primary electron beams to asample. Such a combination makes it possible to increase the throughput(the number of samples inspected per unit time) at the inspection step.

The multi-purpose electron beam inspection system for defect inspectionaccording to this embodiment will be described below more specificallywith reference to the accompanying drawings.

FIG. 11 is a schematic view showing a multi-purpose electron beaminspection system 2030. The multi-purpose electron beam inspectionsystem 2030 has a optical column 2028 containing an electron gun 2001for generating a primary electron beam 2102. The multi-purpose electronbeam inspection system 2030 further has a shield casing 2029 coveringthe lower part of the optical column 2028. The shield casing 2029accommodates a wafer (sample) 2110. The shield casing 2029 iscommunicated with the lower part of the optical column 2028 andevacuated to create a vacuum therein as in the case of the inside of theoptical column 2028. The optical column 2028 contains, in addition tothe electron gun 2001, condenser lenses 2002, 2003 and 2004 forirradiating the primary electron beam 2102 to the surface of the wafer2110, a rectangular aperture 2005, a circular aperture 2006, a deflector2007, a Wien filter 2009, lens systems 2012, 2010, 2015 and 2017 actingon secondary electrons emitted from the surface of the wafer 2110irradiated with the primary electron beam 2102, a microchannel plate2018, a scintillator 2018′, and an optical fiber bundle 2019. When madeof a stainless steel, the shield casing 2029 needs magnetic shielding.When made of a ferromagnetic material, the shield casing 2029 candispense with magnetic shielding.

In the electron beam inspection system 2030, the primary electron beam2102 emitted from the electron gun 2001 is irradiated to the surface ofthe wafer (sample) 1110 through the condenser lenses 2002, 2003 and2004, the rectangular aperture 2005, the circular aperture 2006, thelenses 2024 and 2025, the deflector 2007, the Wien filter 2009, and soforth. The primary electron beam 2102 emitted from the electron gun 2001is converged through the condenser lenses 2002, 2003 and 2004 and isincident to the rectangular aperture 2005 or the circular aperture 2006behind it with a uniform intensity. In the system shown in FIG. 11, ademagnified image of the rectangular aperture 2005 or a demagnifiedimage of the circular aperture 2006 or a demagnified crossover image canbe selectively formed on the surface of the wafer 2110 by adjusting thelenses 2024 and 2025. In addition, the wafer surface can be scanned withthe primary electron beam 2102 by activating the deflector 2007.

In the electron beam inspection system 2030 shown in FIG. 11, an imageof the wafer surface is produced as follows. Secondary electrons emittedfrom the surface of the wafer 2110 irradiated with the primary electronbeam 2102 are focused onto the microchannel plate 2018 through the lenssystems 2012, 2010, 2015 and 2017 and converted into an image of lightby the scintillator 2018′ on the rear side of the microchannel plate2018. The light image is taken to the outside through the optical fiberbundles 2019 and 2020 and converted into an electric signal by atwo-dimensional CCD 2027. Thus, an image is produced. The produced imageis compared with pattern data (automatic pattern alignment procedure).Alternatively, images produced at the same positions on adjacent dies(i.e. adjacent chips fabricated on the same wafer) are compared witheach other. That is, the adjacent dice are compared with each other(defect comparison system). Thus, it is possible to automatically detecta possible defect and output the position of a detected defect (defectpost-processing system). Thus, the electron beam inspection system 2030has the function of the image projection type electron beam inspectionsystem.

In the electron beam inspection system 2030 shown in FIG. 11, thebrightness of a monitor 2023 is modulated as follows. A specific voltageis applied to the lens system 2012 adjacent to the surface of the wafer2110, thereby directing the path 2014 of the secondary electrons towarda secondary electron multiplier 2021 adjacent to the edge of the wafersurface. Thus, the secondary electrons are multiplied in the secondaryelectron multiplier 2021 to obtain an electric signal, which is thenamplified by an amplifier 2022 to use it for the brightness modulationof the monitor 2023.

In the multi-purpose electron beam inspection system 2030 shown in FIG.11, inspection for a defect on the wafer surface may be performed asfollows. The deflector 2007 is activated to scan the monitor 2023 withthe beam synchronously with the scanning of the surface of the wafer2110 with the primary electron beam 2102. The image thus obtained, thatis, SEM image, and a pattern data image are compared with each other todetect a possible defect on the wafer surface. Thus, the electron beaminspection system 2030 also has the function of the electron beaminspection system using the scanning electron beam system (SEM system).Accordingly, if the wafer surface is scanned with the primary electronbeam in the direction of the short side of a rectangular pattern, forexample, by activating the deflector 2007, the line width of patternlines arrayed along the long-side direction of the pattern can bemeasured on the basis of the secondary electron image obtained by themonitor 2023.

Further, regardless of whether the electron beam inspection system 2030is used as an image projection type inspection system or as a scanningelectron beam type inspection system, the pattern electric potential canbe evaluated. That is, a negative electric potential is applied to theelectrode 2012 a closest to the wafer 2110 among the electrodes in thelens system 2012 adjacent to the surface of the wafer 2110, wherebysecondary electrons emitted from a pattern on the wafer surface that hasa high electric potential are selectively driven back toward the wafer2110, thereby evaluating the electric potential of the pattern. Thus, itis possible to perform even more accurate inspection for electricalconduction failures (opens, shorts, etc.), that is, contact failures,occurring in the wafer 2110.

The electron beam inspection system 2030 can be switched between theimage projection type inspection system and the scanning electron beamtype inspection system by operating a controller 2900.

The multi-purpose electron beam inspection system according to thisembodiment can perform multi-purpose inspection and measurement, i.e.defect detection, defect review, pattern line width measurement, andpattern electric potential measurement, by itself as stated above.Therefore, it does not occupy a wide floor area in the clean room.Accordingly, an increased number of device fabrication systems can beinstalled in the clean room. Thus, the clean room can be utilizedeffectively.

Next, a further embodiment of the image projection type electron beaminspection system will be described. The electron beam inspection systemaccording to this embodiment is suitable for performing shapeobservation and defect inspection of high-density patterns having aminimum line width of 0.1 micron or less, with high accuracy and highreliability.

As stated above, with the achievement of high-integration densitysemiconductor devices, it has become necessary to inspect the surfacesof substrates, e.g. semiconductor wafers, for defects with highaccuracy. To meet the demand, an image projection type electron beaminspection system has been proposed. The system operates as follows. Thesurface of a sample is irradiated with a primary electron beam from anelectron gun. A secondary electron beam generated from the sample by theelectron beam irradiation is focused onto a microchannel plate tomultiply the secondary electrons. Thereafter, the secondary electronbeam is converted into light representing the intensity of the secondaryelectron beam by a scintillator. The light is detected and convertedinto an electric signal by a TDI-CCD. The electric signal issynchronized with the scanning of the sample, thereby obtainingcontinuous images.

However, the image projection type electron beam inspection systemrequires that the stage moving direction should be made coincident withthe light-receiving surface array direction of the TDI-CCD with highaccuracy. The alignment accuracy depends on mechanical accuracy such asprocessing accuracy at the time of fabrication and assembling accuracy.However, it is difficult with the related art to attain the necessaryaccuracy for recent systems intended to perform shape observation anddefect inspection of high-density patterns having a minimum line widthof 0.1 micron or less.

An object of this embodiment is to provide an electron beam inspectionsystem allowing high-precision alignment between the sample scanningdirection and the TDI-CCD light-receiving surface array direction, whichhas heretofore been impossible to attain owing to the dependence on themechanical accuracy, thereby making it possible to perform shapeobservation and defect inspection with high reliability.

Accordingly, the image projection type electron beam inspection systemfor defect inspection according to this embodiment has an electronirradiation unit for irradiating a sample with a primary electron beam,an optical system for optically processing a secondary electron beamgenerated from the sample by the primary electron beam irradiation toproduce an image of the sample, a microchannel plate for receiving thesample image, a CCD for converting the light signal into an electricsignal after a scintillator converts the output of the microchannelplate into a light signal, an image display unit for processing theoutput of the CCD, and a stage for moving the sample which is used toscan the sample. Between the sample and the microchannel plate, amagnetic lens is positioned to rotate the image.

The magnetic lens may be positioned between a lens in the final stage ofthe optical system and the microchannel plate.

The magnetic lens may be disposed at the crossover position closest tothe microchannel plate.

The magnetic lens may be disposed at the image-formation positionclosest to the final-stage lens on the side of the final-stage lensremote from the microchannel plate.

FIG. 12 is a diagram schematically showing the arrangement of theelectron beam inspection system according to this embodiment. Theelectron beam inspection system is implemented as an image projectiontype electron beam inspection system. In the figure, the electron beaminspection system has an electron gun 3001. A primary electron beam 3002emitted from the electron gun 3001 is shaped through a rectangularaperture and enters a Wien filter 3007 having electrodes 3005 andmagnets 3006 through lenses 3003 and 3004 arranged in two stages. Atthis time, the primary electron beam 3002 is focused onto the plane ofthe Wien filter 3007 as a rectangular primary electron image having asize of 1 mm by 0.25 mm, for example. The optical axis of the primaryelectron beam 3002 is deflected by the Wien filter 3007. Then, theprimary electron beam 3002 passes through lenses 3008 and 3009, therebybeing reduced to ⅕ in size. Thereafter, the primary electron beam 3002is irradiated perpendicularly or normally onto a sample 3010 on a stageS. The sample 3010 is a wafer, for example, which has circuit patternsformed on the surface thereof.

Irradiation with the primary electron beam 3002 causes a secondaryelectron beam 3011 to be emitted from the surface of the sample 3010. Inaddition, a part of the primary electron beam 3002 is reflected at thesurface of the sample 3010. The reflected electron beam and thesecondary electron beam 3011 contain information representing a circuitpattern on the sample 3010. The secondary electron beam 3011 passesthrough the lenses 3009 and 3008 and travels straight through the Wienfilter 3007. Then, the secondary electron beam 3011 travels along a pathoff the path of the primary electron beam 3002 and passes through lenses3012 and 3013 of an electrostatic lens system. The secondary electronbeam 3011 is magnified by the lenses 3009, 3008, 3012 and 3013.

The secondary electron beam 3011 emerging from the final-stage lens 3013of the electrostatic lens system passes through a magnetic lens 3014before being focused onto a microchannel plate 3015 as a rectangularimage. The reason why the magnetic lens 3014 is provided will bedescribed later. The rectangular image thus formed is intensified 10,000times by the microchannel plate 3015 to irradiate a fluorescent unit3016. Consequently, the fluorescent unit 3016 converts the intensifiedrectangular image into light. The light thus obtained passes through arelay optical system 3017 to be applied to a TDI-CCD 3018. The TDI-CCD3018 converts the incident light into an electric signal synchronizedwith the scanning speed at which the sample 3010 is scanned by themoving stage and gives the electric signal to an image processing unit3019 as a continuous image.

The image thus acquired by the image processing unit 3019 is used todetect a possible defect on the surface of the sample 3010 by on-timecomparison between the images of a plurality of cells or comparisonbetween the images of a plurality of dice. The configurational featureof a defect on the sample 3010 detected in the image processing unit3019 and the number of defects detected, together with the coordinatesof defect locations, etc., are displayed on a CRT and also recorded asthe occasion demands.

It is desirable to perform the above-described shape observation anddefect inspection of the sample surface by taking into consideration thefact that the substrates of different samples 3010 have differentsurface structures because various films, e.g. an oxide film and anitride film, may be used, and the fact that the observation andinspection may be performed at different process steps. That is, it isdesirable to irradiate charged particles to the sample 3010 underappropriate conditions to effect irradiation under optimum conditionsand thereafter acquire an image to perform shape observation and defectinspection.

Although not only an image of secondary electrons but also an image ofback scattered electrons and reflected electrons can be acquired asstated above, this embodiment is described with regard to a case where asecondary electron image is acquired for shape observation and defectinspection.

The operating principle of the magnetic lens 3014 shown in FIG. 12 isexplained by using FIGS. 13(A) and 13(B). The magnetic lens 3014 has anannular configuration as seen from above, and its cross-section hasU-shaped configurations at the left and right ends thereof. FIGS. 13(A)and 13(B) show only the central portion of the magnetic lens 3014. Asshown in FIGS. 13(A) and 13(B), when the secondary electron beam 3011passes through the center of the pole pieces of the magnetic lens 3014,a magnetic path is formed to extend through the upper pole piece 3021 aand the lower pole piece 3021 b by an annular coil (not shown) providedbetween the upper and lower pole pieces 3021 a and 3021 b. Thus, amagnetic field is applied to the secondary electron beam 3011. Thiscauses the secondary electron beam 3011 to be rotated in the directionindicated by the arrow 3022 with respect to the center of the opticalaxis of the secondary electron beam 3011. The amount of rotation of thesecondary electron beam 3011 increases as the magnetic field applied tothe secondary electron beam 3011 through the pole pieces 3021 a and 3021b is intensified.

The above-described principle may be utilized as follows. The magneticlens 3014 is positioned between the lens 3013 and the microchannel plate3015, for example, and the intensity of the magnetic field produced bythe magnetic lens 3014 is controlled. By doing so, it is possible torotate the image formed on the microchannel plate 3015 by the secondaryelectron beam 3011 emitted from the sample 3010. Accordingly,controlling the intensity of the magnetic field produced by the magneticlens 3014 allows the scanning direction of the sample 3010 as scanned bythe moving stage S to coincide with the integration direction on thelight-receiving surface of the TDI-CCD 3018.

If the magnetic lens 3014 is positioned between the lens 3013 in thefinal stage of the electrostatic lens system and the microchannel plate3015, the secondary electron beam 3011 and hence the image formed on themicrochannel plate 3015 can be rotated by the magnetic lens 3014 withoutexerting any effect on the electrostatic lens system (e.g. an undesiredchange in the magnification of the electrostatic lens system, orintroduction of aberration or distortion into the image).

We actually positioned the magnetic lens 3014 between the final-stagelens 3013 and the microchannel plate 3015 as shown in FIG. 12. After thescanning direction of the sample 3010 and the light-receiving surfacearray direction of the TDI-CCD 3018 had been mechanically aligned inadvance so that the angular displacement between the two directions waswithin ±1 degree, the rotational angle of the secondary electron beam3011 was measured at various magnetic field strengths of the magneticlens 3014. The results of the measurement revealed that the secondaryelectron beam 3011 can be rotated in the range of angles of ±10 seconds.That is, it is only necessary for the angle accuracy to satisfy therelationship of (field size/2)×(angle accuracy)<( 1/10)×(pixel size).Hence, the angle accuracy<( 1/2048×5)rad=9.77×10⁻⁵ rad=20.2 seconds.

It is desirable that the above-described magnetic lens 3014 should beprovided at the position shown in FIG. 14 or 15. In FIG. 14, themagnetic lens 3014 is positioned at the crossover position 3031 closestto the final-stage lens 3013 of the electrostatic lens system betweenthe lens 3013 and the microchannel plate 3015, as has been stated above.This arrangement makes it possible to utilize the action of the magneticlens 3014 to rotate the secondary electron beam 3011. Moreover, theinfluence on the focusing conditions of the electrostatic lens system inthe image projection system can be reduced to a substantially ignorablelevel.

In FIG. 15, the magnetic lens 3014 is provided at the image-formationposition 3041 closest to the final-stage lens 3013 of the electrostaticlens system on the side of the lens 3013 remote from the microchannelplate 3015. The image-formation position 3041 is conjugate to thesurface of the sample 3010 and also to the secondary electron beamincident surface of the microchannel plate 3015. The image-formationposition 3041 is where no lens action other than the rotating action ofthe magnetic lens 3014 takes place. Therefore, the magnetic lens 3014only acts to correct the displacement between the scanning direction ofthe sample 3010 and the light-receiving surface array direction of theTDI-CCD 3018. In other words, such directional displacement can becorrected easily by the magnetic lens 3014. Further, because therotating action of the magnetic lens 3014 exerts no influence on theelectrostatic lens system of the image projection system and hencecauses no aberration or distortion, the arrangement shown in FIG. 15 canattain a high degree of accuracy, which is equal to or higher than theaccuracy obtained by the arrangement shown in FIG. 14.

As will be understood from the foregoing description of the electronbeam inspection system, the present embodiment allows the samplescanning direction and the light-receiving surface array direction ofthe TDI-CCD to be readily aligned with each other. Therefore, it ispossible to eliminate or minimize the image blur due to discrepancybetween the two directions. Thus, it becomes possible to effect shapeobservation and defect inspection with high reliability at excellentresolution, i.e. 0.1 micron or less.

Further, in this embodiment, even if the number of stages of the TDI-CCDis increased, image blur as caused by discrepancy between the samplescanning direction and the TDI-CCD light-receiving surface arraydirection is minimized. Therefore, it is possible to use a TDI-CCD withan increased number of stages and hence possible to provide an electronbeam inspection system exhibiting even higher sensitivity. Accordingly,high throughput can be realized.

Next, a further embodiment of the electron beam inspection system willbe described. This embodiment relates to an electron beam inspectionsystem that evaluates the surface of a solid sample by using a single orplurality of electron beams. More particularly, the embodiment relatesto an electron beam inspection system capable of evaluating samples,e.g. wafers or masks, having patterns with a minimum line width is 0.1μm or less, with high throughput (i.e. the number of samples evaluatedper unit time), high accuracy and high reliability. Items of evaluationinclude defect inspection of a sample, e.g. a semiconductor wafer, linewidth measurement, overlay accuracy measurement, voltage contrastmeasurement at high time resolution, and so forth. The voltage contrastmeasurement allows inspection for an electrical defect under the wafersurface and measurement of small particles on the wafer surface.

In this embodiment, the dimension D of the electron beam means thediametrical dimension (diameter of diagonal line length) of the electronbeam image on the sample surface. Further, in this embodiment, thespacing between electron beams means the distance between the centers ofadjacent electron beam images on the sample surface.

First, a technique relating to the electron beam inspection systemaccording to this embodiment will be described.

This type of electron beam inspection system for evaluating defects on asample, e.g. a wafer, is disclosed, for example, in Japanese PatentApplication Unexamined Publication (KOKAI) No. Hei 9-311112. Thispublication discloses a pattern inspection system in which a primaryelectron beam is applied to a sample formed with a pattern, e.g. a maskor a wafer, and secondary electrons emitted from the sample are used toinspect the pattern on the sample. Further, in the related art, adecelerating electric field is applied between an objective and thesample to narrow down the primary electron beam and the sample isirradiated with the narrowed electron beam, thereby efficientlydetecting secondary electrons emitted from the sample. In addition, therelated art uses a secondary electron energy filter comprising ahemispheric mesh electrode to measure the electric potential contrast ofthe pattern on the sample surface.

A decelerating electric field type objective used in the above-describedrelated art allows all secondary electrons to pass through it. Thismakes it difficult to measure the voltage contrast. The secondaryelectron filter comprising a hemispheric mesh electrode has thefollowing problems: If the mesh electrode is provided between theobjective and the sample, the image plane distance of the objective lensincrease, and the axial chromatic aberration coefficient increases. Inaddition, the primary electron beam cannot be focussed, or the beamcurrent decreases as the primary electron beam is narrowed down.Further, the mesh electrode irregularly bends the path of the primaryelectron beam passing near the mesh electrode. Therefore, the beam maybe blurred, or scanning distortion may occur.

This embodiment is made in view of the above-described problems of therelated art. Accordingly, an object of this embodiment is to provide anelectron beam inspection system capable of obtaining a large beamcurrent while narrowing down the primary electron beam and hence capableof measuring the voltage contrast and free from scanning distortion.

The electron beam inspection system according to this embodiment uses aunipotential electrostatic lens having at least three axially symmetricelectrodes: an electrode closer to the electron gun (i.e. upperelectrode); an electrode closer to the sample (i.e. sample-sideelectrode, or lower electrode); and a center electrode between the upperand lower electrodes. With the electrostatic lens, a primary electronbeam is focused onto the sample surface, and the sample surface isscanned with the primary electron beam by using a deflector. Secondaryelectrons emitted from the sample by the primary electron beamirradiation are detected to evaluate the sample surface. The electronbeam inspection system applies a voltage lower than the electricpotential at the sample surface to the lower electrode, therebyobtaining the electric potential contrast of the pattern on the samplesurface.

In the electron beam inspection system according to this embodiment,when evaluation that need not obtain the electric potential contrast isto be performed, a voltage close to the ground potential is applied tothe sample-side electrode (lower electrode). When the voltage applied tothe lower electrode is changed to a considerable extent, the focusingconditions are adjusted by varying a positive high voltage applied tothe center electrode.

In the electron beam inspection system according to this embodiment,when the focusing conditions are changed slightly at high speed, thevoltage applied to the electrode of the electrostatic lens that iscloser to the electron gun than the center electrode (i.e. the voltageapplied to the upper electrode) is controlled. In this embodiment, acontrast image is obtained from changes in the emission of secondaryelectrons from the sample surface under application of an electricpotential distribution.

The subject matter of this embodiment will be described below morespecifically with reference to the accompanying drawings. FIG. 16 is adiagram schematically showing the arrangement of the electron beaminspection system according to this embodiment. As shown in FIG. 16, anelectron gun 4020 has a cathode 4022 placed in a Wehnelt cylinder 4021and an anode 4023 provided below the Wehnelt cylinder 4021. A primaryelectron beam is emitted from the cathode 4022 toward the anode 4023.After passing through the anode 4023, the electron beam is aligned byaligning deflectors 4024 and 4025 so as to pass through the centers ofcondenser lenses 4034, 4035 and 4036.

When the cathode 4022 is a thermal field emission cathode (TEF cathode),the primary electron beam emitted from the cathode 4022 is controlled bythe condenser lenses 4034, 4035 and 4036 to adjust the image-formationmagnification at the sample surface. The controlled primary electronbeam 4016 is focused onto the surface of a sample 4033 by objectivelenses 4032, 4038 and 4039. The primary electron beam 4016 forms acrossover image on the deflection center plane of an E×B separator 4030.The primary electron beam 4016 is deflected in two stages by anelectrostatic deflector 4027 and an electromagnetic deflector 4029 inthe E×B separator 4030 to raster-scan over the surface of the sample4033.

In the electron beam inspection system shown in FIG. 16, inspection ofthe sample 4033 is performed by scanning a predetermined width of thesurface of the sample 4033 in the x-direction (direction perpendicularto the plane of FIG. 16) with the primary electron beam and, while doingso, continuously moving a stage 4041 in the y-direction. Upon completionof the inspection of a predetermined region of the sample 4033 as far asthe end in the y-direction, the stage 4041 is moved in the x-directionby a predetermined width or by a width slightly larger than thepredetermined width to inspect a neighboring stripe (a region adjacentto the predetermined region). As the result of the primary electron beam4016 irradiating the surface of the sample 4033 by raster scan,secondary electrons are emitted from the scanning points on the sample4033.

Secondary electrons emitted from the irradiated points on the sample4033 are extracted toward the electron gun 4020 by an acceleratingelectric field for the secondary electrons that is formed by the highvoltage applied to the center electrode 4039 of the objective 4031 andthe ground potential at the upper electrode 4038 and the lower electrode4032, together with the negative high voltage applied to the sample4033. The secondary electrons are deflected from the primary opticalsystem by the E×B separator 4030 so as to travel along the path in thedirection indicated by the dotted line 18 in FIG. 16. Then, thesecondary electrons are detected with a secondary electron beam detector4028, and thus an SEM image (scanning electron microscope image) isformed. To evaluate the electric potential contrast of the sample 4033,a voltage lower than the electric potential at the sample 4033 isapplied to the sample-side electrode 4032 of the objective 4031, therebymaking the axial potential distribution lower than the potential at thesample surface as shown in FIG. 18 (described below). A controller 4900shown in FIG. 16 allows a desired voltage to be applied to each of theupper electrode 4038, the center electrode 4039 and the lower electrode4032.

FIG. 18 shows the distribution of axial potential when 4.5 kV, 8 kV, 350V and 500 V are applied to the upper electrode 4038, the centerelectrode 4039, the lower electrode 4032 and the sample 4033,respectively. In FIG. 18, the abscissa axis represents the distancealong a Z-axis, i.e. an axis extending perpendicularly to the surface ofthe sample 4033. The point of 0 mm, as a fiducial point, is theintersection between the axis and a line extending from the upperelectrode 4038 at right angles to the axis. Accordingly, 4.000 mm in thefigure shows the distance from the intersection. In FIG. 18, the sample4033 (not shown in the figure) is placed at a position corresponding tothe point 4002, and the lower electrode 4032 (not shown in the figure)is provided at a position corresponding to the middle between the point4001 and the point 4002. The center electrode 4039 is provided at aposition corresponding to the point 4003. Because a voltage lower thanthe sample potential is applied to the lower electrode 4032, the axialpotential is lower than the electric potential at the surface of thesample 4033 over the range of from the point 4001 to the point 4002.Among the secondary electrons, those emitted from a pattern having ahigh electric potential have low potential energy and hence low speed.Therefore, such secondary electrons are driven back toward the sample4033 by the potential barrier between the point 4001 and the point 4002.Accordingly, these secondary electrons are not detected. On the otherhand, secondary electrons emitted from a pattern having a low electricpotential have high potential energy and hence high speed. Therefore,these secondary electrons pass the potential barrier and reach thedetector 4028.

When an electric potential lower than the sample potential is applied tothe sample-side (lower) electrode 4032, a large electric field isgenerated between the center electrode 4039 and the lower electrode4032. Therefore, the spacing between the center and lower electrodes4039 and 4032 should preferably be set wider than the spacing betweenthe upper electrode 4038 and the center electrode 4039. Further, thelarge electric field formed between the center electrode 4039 and thelower electrode 4032 causes the lens action to become excessivelystrong, resulting in a large deviation of the focusing conditions. Tocorrect the deviation, the positive high voltage applied to the centerelectrode 4039 should be lowered to a considerable extent.

Regarding the lens structure (condenser lenses 4034, 4035 and 4036) inthe electron beam inspection system shown in FIG. 16, it is preferableto form the condenser lenses 4034, 4035 and 4036 by cutting an integralceramic member 4026 and selectively coating the surface thereof with ametal to form electrodes. By doing so, the outer diameter of an opticalcolumn 4040 can be reduced. FIG. 17 shows the way in which opticalcolumn 4040 with a reduced outer diameter are arranged in two rows eachconsisting of four optical column. In the example shown in FIG. 17,eight optical column 4040 are positioned above an 8-inch wafer in such amanner that each secondary electron beam detector 4028 is directed to aside where it will not interfere with neighboring optical systems. Ifevaluation is performed by using eight optical column 4040 (each havingan outer diameter of 40 mm or less, for example) arranged as shown inFIG. 17 and moving the sample stage 4041 in the y-direction, it ispossible to obtain throughput (i.e. the number of samples processed perunit time) 8 times as high as that in the case of using a single opticalcolumn 4040.

In a case where an image is produced on the basis of pattern steps or adifference in material, the secondary electron detection efficiencyshould preferably be increased. In such a case, an electric potentialclose to the ground potential should be applied to the sample-sideelectrode 4032. At that time, a positive high voltage is applied to thecenter electrode 4039. In a case where focusing is effected dynamicallyto respond to the unevenness and so forth of the sample surface, thevoltage applied to the upper electrode 4038, which is close to theground potential, is controlled. In this case, the control voltage canbe changed at high speed.

Although the electron beam inspection system according to thisembodiment has been described as a scanning electron beam (SEM) typeinspection system, it should be noted that the featuring portions ofthis embodiment are also applicable to an image projection type electronbeam inspection system.

In the electron beam inspection system according to this embodiment, avoltage lower than the electric potential at the sample surface isapplied to the sample-side electrode of an electrostatic lens havingthree axially symmetric electrodes, whereby the electron beam inspectionsystem is made free from the problems that the image plane distance ofthe objective lengthens and hence the axial chromatic aberrationcoefficient increases, and that the primary electron beam cannot benarrowed down. In this case, the primary electron beam is kept focusedonto the sample surface by varying the positive high voltage applied tothe center electrode. When it is unnecessary to obtain the electricpotential contrast, a voltage close to the ground potential is appliedto the sample-side electrode. By doing so, the detection of secondaryelectrons can be performed efficiently.

Next, a further embodiment of the present invention will be described.This embodiment relates to a charged particle beam system for applyingan electron beam as a charged particle beam to a sample placed on a two-or three-dimensionally movable stage (hereinafter referred to as simply“stage”) and also relates to a method of conveying a sample to thestage.

First, a technique relating to the charged particle beam systemaccording to this embodiment will be described.

In an electron beam system as this type of charged particle beam systemthat irradiates a charged particle beam to a sample placed on a stage,the whole stage is installed in a vacuum container because of thenecessity to place the whole charged beam path in a vacuum environment.Further, in order to allow the stage to function in a vacuum, it isnecessary to give special consideration to the support structure andlubrication for the actuator and guide mechanism of the stage, thematerial of the stage, and so forth, unlike an arrangement in which thestage is operated in the atmospheric environment.

Regarding the actuator, for example, when a servomotor is placed in avacuum, it needs to be designed to meet high-temperature specificationsbecause it is difficult to effect heat dissipation under vacuum. It isalso necessary to impose restrictions on the use conditions of theservomotor and to use a solid lubricant or vacuum grease for lubricationof the rotating shaft. When the servomotor is placed on the atmosphereside, it is necessary to provide a vacuum seal mechanism, e.g. amagnetic fluid seal, in the rotation inlet part and to provide the stagewith another guide in addition to an X-direction guide and a Y-directionguide to thereby construct a structure in which the servomotor need notmove together with the X-direction guide or the Y-direction guide.Consequently, the structure is complicated and large in size incomparison to the stage operating in the atmospheric environment.

Regarding the support structure for the guide mechanism, an air bearingutilizing hydrostatic pressure as used for a high-precision stage usedin the atmospheric environment cannot be used under vacuum environmentalconditions. In the case of using a high-precision rolling bearing, e.g.a cross rolling bearing, it is also necessary to use vacuum grease or afluorine-containing lubricant of low vapor pressure, which are inferiorin lubricating properties to lubricants used in the atmosphericenvironment. For these reasons, it has heretofore been difficult toproduce a high-precision stage for use under vacuum.

Regarding the material of the stage, it is necessary to select amaterial that emits a minimum amount of gas in a vacuum. An aluminummaterial is not frequently used. Further, it has heretofore beennecessary to give special consideration to the finishing of the surfacesof the components in order to minimize the surface area of the material.

The stage mechanism for use in a vacuum requires the followingconstituent elements in addition to those stated above: a vacuumcontainer for containing the stage; a load-lock chamber for transferringa sample from an atmospheric environment to a vacuum environment; avacuum transfer mechanism for conveying the sample under vacuum; vacuumpiping for the vacuum container; valves; and a vacuum pump.

Because the sample is placed in a vacuum, a vacuum chuck, which usessuction force, cannot be used as a device for holding the sample.Accordingly, it has heretofore been necessary to use an electrostaticchuck or a mechanical chuck that holds the rear surface or side of thesample with a holding member. However, the electrostatic chuck hasproblems that it is costly and likely to adsorb particles, and that acertain type of electrostatic chuck requires time to effectdestaticization. On the other hand, the mechanical chuck is incapable ofholding the sample flat and needs to hold the rear surface or side ofthe sample with a holding member. Therefore, the mechanical chuck cannotmeet the semiconductor manufacturers' demands that the chuck should notbe brought into contact with any portion of the wafer, as a sample,other than the back thereof.

As has been stated above, the charged particle beam system according tothe related art requires that the stage should be provided in a vacuumenvironment. Therefore, the system suffers a high production cost andrequires a large installation area and occupied area. Further, themechanism is complicated, and the maintenance of the system isdifficult.

In general, when an object that has been exposed to the atmospheric airis subjected to evacuation, gas molecules adsorbed on the object surfaceare released. Therefore, some evacuation time is required to obtain apredetermined degree of vacuum. Most of the released gas is watermolecules (i.e. water vapor adsorbed on the object surface in theatmospheric environment) in a high degree of vacuum. Accordingly, when asample that has been exposed to the atmospheric air is carried in acharged particle beam irradiation area without being satisfactorilyevacuated, gas molecules adsorbed on the sample surface are releasedjust as the sample is carried in the vacuum environment at the chargedparticle beam irradiation area, degrading the degree of vacuum at thecharged particle beam irradiation area. Thus, the conventional systemalso has a problem that processing cannot be carried out with thedesired performance. Accordingly, it has been demanded that the amountof gas released from the sample surface and the surfaces of componentsof the stage into the charged particle beam irradiation area should bereduced to a considerable extent and the released gas should beevacuated rapidly.

An purpose of this embodiment is to allow a charged particle beam systemto be produced in a compact structure and at reduced costs by providingmechanical structures such as the actuator and guide mechanism of thestage in the atmospheric environment.

Another purpose of this embodiment is to prevent the sample and thecharged particle beam optical system from being contaminated withparticles or released gas by arranging the charged particle beam systemsuch that only a place where a vacuum environment is required, i.e.where the sample and charged particle beam optical system are placed, ismaintained under vacuum.

A further purpose of this embodiment is to provide a charged particlebeam system designed so that the amount of gas released into a vacuumfrom the sample surface and the surfaces of the stage components can bereduced to a considerably smaller value than in the case of theconventional system.

A still further purpose of this embodiment is to provide a method ofconveying a sample to the inside of a charged particle beam systemdesigned so that the amount of gas released into a vacuum from thesample surface and the surfaces of the stage components can be reducedconsiderably in comparison to the conventional system.

A charged particle beam system according to this embodiment irradiate acharged particle beam to the surface of a sample placed on a stage. Inorder that only a place where the charged particle beam is irradiatedand its vicinities should be maintained at a predetermined degree ofvacuum, at least one annular differential pumping structure is providedaround a region where the charged particle beam is applied, and furthera structure for blowing an inert gas onto the sample surface is providedat the outer peripheral side of the differential pumping structure. Withthe described arrangement, it is possible to use a stage designed foruse in the atmospheric environment and hence possible to produce thecharged particle beam system in a compact structure and at reducedcosts. Further, it is possible to prevent particles from entering fromthe atmosphere side to adhere to the sample surface. It is also possibleto minimize the number of opportunities for the sample to come in directcontact with the atmospheric air and hence possible to reduce the amountof gas released from the charged particle beam irradiation area.

In a modification of the charged particle beam system according to thisembodiment, the inert gas blowing structure is formed such that theinert gas blown onto the sample surface will flow mainly radiallyoutward from the charged particle beam irradiation area. Thus, thepumping operation of the differential pumping unit is facilitated.Consequently, it becomes possible to form a compact differential pumpingstructure and to use a vacuum pump of small capacity for differentialevacuation.

In another modification of the charged particle beam system, thedifferential pumping structure has a differential pumping passage forhigh vacuum and a differential pumping passage for low vacuum. Thesedifferential pumping passages connect to each other at the downstreamside of the differential pumping structure to perform evacuation throughthe same piping at the downstream side of the junction of the pumpingpassages. At the upstream side of the differential pumping structure,the differential pumping passage for low vacuum offers higher pumpingresistance than that of the differential pumping passage for highvacuum. Thus, it is possible to reduce the number of differentialpumping passages and/or vacuum pumps and hence possible to attainreductions in size and costs of the charged particle beam system.

In another modification of the charged particle beam system, the stageis provided with a mechanism for fine height adjustment so that thesurface of the stage extending under the differential pumping structurecan be flush with the surface of the sample placed on the stage. Thus,there is no step between the sample surface and the stage surface.Consequently, the gap between the differential pumping unit and thestage is kept constant over the whole movable range of the stage.Therefore, it becomes possible to allow the differential pumpingfunction to operate normally over the whole movable range of the stage.

In another modification of the charged particle beam system, either thewhole movable range of a stage adapted to move a sample to apredetermined position or the movable range of the sample is alwayscovered with a vacuum container filled with an inert gas. With thisarrangement, the number of particles entering to adhere to the samplesurface can be further reduced. Further, because the sample surface andthe stage are not exposed to the atmospheric air, it is possible tofurther reduce the amount of gas released into the vacuum from thesample surface and the surfaces of the stage components.

In another modification of the charged particle beam system, thecontainer filled with an inert gas is communicably connected with avacuum container through a block valve, so that a sample is carried inand out of the inert gas-filled container through the vacuum container.In other words, after the sample has been inserted into the vacuumcontainer, the vacuum container is evacuated to a predeterminedpressure. Then, a high-purity inert gas is introduced into the vacuumcontainer. Thereafter, the gate valve is opened, and the sample isplaced on the stage in the container filled with the high-purity inertgas. With the described arrangement and procedure, the sample is firstput in the vacuum container and once subjected to evacuation, therebyallowing a large amount of gas to be released from the sample surfaceand thus cleaning the sample. Thereafter, a high-purity inert gas isintroduced into the vacuum container, and the sample is conveyed to thestage in the high-purity inert gas. Accordingly, when the sample isinserted into the charged particle beam irradiation area and placed inthe vacuum environment, only the high-purity inert gas can be releasedfrom the sample surface. The high-purity inert gas has very smalladsorption energy with respect to the surface of an object. Therefore,the high-purity inert gas is released from the sample surface within anextremely short period of time and hence will not degrade the degree ofvacuum at the charged particle beam irradiation area. Thus, it is easyto maintain the charged particle beam irradiation area at a high degreeof vacuum. It is also possible to minimize the likelihood that thesample surface may be contaminated.

In another modification of the charged particle beam system, an inertgas circulating mechanism is provided so that the inert gas blown ontothe sample surface is recovered by a vacuum pump and/or compressor andthen pressurized so as to be blown onto the sample surface again. Thus,the high-purity inert gas can be recycled and hence economized. Further,because the high-purity inert gas is not discharged into the room wherethe present system is installed, it is possible to eliminate the dangerof accident such as suffocation by the high-purity inert gas. Examplesof inert gases usable in this embodiment include nitrogen (N₂), argon(Ar), xenon (Xe) and the like.

Another modification of this embodiment provides a sample transportingmethod. That is, the method includes the following steps: preparing acharged particle beam system wherein a container filled with an inertgas is connected with a vacuum container through a gate valve, as statedabove; inserting a sample into the vacuum container of the chargedparticle beam system; evacuating the vacuum container to a predeterminedpressure; introducing an inert gas into the vacuum container; andopening the gate valve and placing the sample onto a stage in thecontainer filled with the inert gas. The method allows the chargedparticle beam irradiation area to be readily maintained at a high degreeof vacuum.

Another modification provides a wafer defect inspection system designedto inspect the surface of a semiconductor wafer for a defect by makinguse of the above-descried charged particle beam system or sampleconveying method. Thus, it is possible to provide a wafer defectinspection system of high reliability that can be produced at reducedcosts and requires minimum installation and foot print.

Another modification provides an exposure system designed to transfer asemiconductor device circuit pattern onto the surface of a semiconductorwafer through exposure by utilizing the above-described charged particlebeam system or sample conveying method. Thus, it is possible to providea charged particle beam exposure system of high reliability that can beproduced at reduced costs and requires minimum installation and occupiedareas.

Another modification provides a semiconductor manufacturing method thatutilizes the above-described charged particle beam system or sampleconveying method. Thus, it is possible to attain reductions in cost ofthe semiconductor fabrication method.

The charged particle beam system according to this embodiment will bedescribed below in detail with reference to the accompanying drawings.

FIG. 19 is a diagram showing an embodiment of the charged particle beamsystem, which is an enlarged view of a part of the charged particle beamsystem. Reference numeral 5001 denotes an optical column having apublicly known structure for accommodating an optical system forirradiating a charged particle beam 5050 to a sample 5002. Only thedistal end portion of the optical column 5001 is shown in the figure. Adifferential pumping unit 5004 is installed in such a manner as tosurround the end portion of the optical column 5001. The differentialpumping unit 5004 has a hole 5041 in the center thereof. The hole 5041needs to be sufficiently large to pass the charged particle beam 5050without affecting any influence thereon. The sample 5002 is placed on astage 5003. The sample 5002 moves together with the stage 5003. Theoptical column 5001 is secured to a frame (see FIG. 24) of the systemsuch that a small gap of the order of from several microns to severalhundred microns is maintained between the differential pumping unit 5004and the surface 5021 of the sample 5002 (hereinafter referred to as“sample surface 5021”). It should be noted that the optical system inthe optical column 5001 is not the gist of the present invention.Therefore, a detailed description thereof is omitted.

The differential pumping unit 5004 has annular grooves 5005 and 5006 fordifferential pumping provided in order from the center toward theradially outer side. The annular groove 5005 is communicated with vacuumpiping 5008. The annular groove 5006 is communicated with vacuum piping5009. Gas flowing in toward the charged particle beam 5050 from theouter peripheral side of the differential evacuation unit 5004 isevacuated through the annular grooves 5005 and 5006, whereby the flowrate of gas leaking to the charged particle beam irradiation area isreduced below the allowable level, thereby maintaining the chargedparticle beam irradiation area at a predetermined degree of vacuum.Therefore, the configuration of the annular groove 5005, theconfiguration of the evacuation flow path of the annular groove 5005,the gap 5051 between the sample surface 5021 and the differentialevacuation unit 5004 and the performances of the vacuum piping and thevacuum pump are determined appropriately so that the annular groove 5005is higher in the degree of vacuum than the annular groove 5006 and theflow rate of gas leaking to the charged particle beam irradiation areais below the allowable level, or that the annular groove 5005 is higherin the degree of vacuum than the charged particle beam irradiation area.Annular grooves for performing differential pumping constitute adifferential pumping structure. In FIG. 19, the annular grooves areformed in a concentric double-groove configuration. However, the presentinvention is not necessarily limited to the double-groove configuration.The differential pumping structure may be formed from a single annulargroove or three or more concentric annular grooves, depending on thedegree of vacuum required at the charged particle beam irradiation areaand on the arrangement of the annular grooves, the vacuum piping and soforth.

Another annular groove 5007 is formed at the outer peripheral side ofthe annular groove 5006 of the differential pumping unit 5004. Theannular groove 5007 is communicated with piping 5010. Through the piping5010, a high-purity inert gas is supplied and blown off from the annulargroove 5007 onto the sample surface 5021. A part of the high-purityinert gas blown off from the annular groove 5007 is discharged to thecharged particle beam irradiation area by suction acting through theannular groove 5006. The rest of the high-purity inert gas flows in theopposite direction and is discharged to the outside from the outerperiphery of the differential pumping unit 5004. Thus, the high-purityinert gas flows outward to act as a shield. Therefore, the atmosphericair is prevented from flowing into the charged particle beam irradiationarea by the outward flow of the high-purity inert gas. If the shieldmechanism effected by the high-purity inert gas is not provided, theoutside air flows into the area between the sample surface 5021 and thedifferential pumping unit 5004. Consequently, particles and water vaporin the atmospheric air may enter the charged particle beam irradiationarea and contaminate the sample surface 5021 and the lenses in theoptical column 5001, which adversely affects such operations asinspection of the wafer surface using a charged particle beam andtransfer of a pattern onto the wafer surface by exposure. In thisregard, the provision of a high-purity inert gas blowing mechanism as inthe present invention makes it possible to prevent entry of particlesand water vapor in the atmospheric air and hence eliminates thelikelihood of the sample and the lenses being contaminated. Accordingly,operations such as wafer inspection and exposure can be carried outwithout any problem.

It should be noted that if the outer peripheral portion of thedifferential pumping unit 5004 is extended outwardly as shown byreference numeral 5004 a (see FIG. 20) to thereby increase the areacovering the sample surface 5021, it is possible to prevent the entry ofparticles and water vapor even more surely and effectively.

FIG. 20 shows a modification of the charged particle beam system. Inthis modification, a high-purity inert gas outlet 5007 a is directedtoward the outer peripheral side. Consequently, the gas forcibly flowsradially outward in the direction of the arrow A between the samplesurface 5021 and the differential pumping unit 5004. If the high-purityinert gas outlet 5007 a is formed as stated above and the high-purityinert gas supply pressure is raised to an appropriate value with respectto the atmospheric pressure to thereby set the velocity of thehigh-purity inert gas flow from the outlet 5007 a to an appropriatevalue, the flow of the high-purity inert gas acts as an ejector, and aflow such as that indicated by the arrow B occurs. Accordingly, theinner peripheral side of the differential pumping unit 5004 can bemaintained at a negative pressure. Thus, it becomes possible to furtherreduce the possibility that contaminants in the outside air, e.g.particles and water vapor, may enter the area between the sample surface5021 and the differential pumping unit 5004. In addition, an pumpingeffect is provided. Accordingly, the load of evacuation on thedifferential pumping mechanism can be reduced. Thus, it is possible toattain reductions in size of the differential pumping unit 5004, thevacuum piping 5008 and 5009 and the vacuum pump.

Further, the differential pumping unit 5004 may be provided with abaking heater BH to heat the differential pumping unit 5004, whereby thegas flowing from the annular grooves 5005 and 5006 to the vacuum piping5008 and 5009 is expanded under heating to increase the evacuationefficiency, thereby enabling a high degree of vacuum to be attained bydifferential evacuation even more easily.

FIG. 21 shows another modification of the charged particle beam system.In this modification, a vacuum chamber 5011 is provided in thedifferential pumping unit 5004. The vacuum chamber 5011 is communicatedwith both a high vacuum-side evacuation passage 5005 a and a lowvacuum-side evacuation passage 5006 a. A high vacuum-side annular groove5005 and a low vacuum-side annular groove 5006 for differentialevacuation are communicated with the high vacuum-side evacuation passage5005 a and the low vacuum-side evacuation passage 5006 a, respectively.The vacuum chamber 5011 is held under vacuum through vacuum piping 5008a.

The low vacuum-side evacuation passage 5006 a is formed with anextremely small conductance relative to that of the high vacuum-sideevacuation passage 5005 a. Accordingly, the downstream-side pressures ofthe evacuation passages 5005 a and 5006 a are both equal to the pressurein the vacuum chamber 5011, that is, equal to each other. However, thepressures in the annular grooves 5005 and 5006, which are upstream theevacuation passages 5005 a and 5006 a, are different from each other toa considerable extent. Thus, the annular groove 5006 maintains a lowvacuum, and the annular groove 5005 maintains a high vacuum, therebyallowing differential pumping to be effected appropriately.

By forming the evacuation passages as stated above, the differentialpumping unit 5004 is allowed to dispense with other vacuum piping thanthe vacuum piping 5008 a. Accordingly, it is possible to attainreductions in size and costs of the system.

FIGS. 22( a) and 22(b) show another modification of the charged particlebeam system. FIG. 22( a) shows a state where the column is positioned inthe vicinity of one end of the stage. FIG. 22( b) shows a state wherethe column is positioned in the vicinity of the other end of the stage.In this embodiment, a sample 5002 is placed on the stage surface 5031,and plate members 5060 and 5061 are mounted around the sample 5002. Theheight of the plate members 5060 and 5061 from the stage surface 5031has previously been adjusted so that the top surfaces 5601 and 5611 ofthe plate members 5060 and 5061 are flush with the sample surface 5021.By mounting such a height adjusting mechanism, the gap 5051′ (or 5051″)between the differential pumping unit 5004′ (or 5004″) and the stagesurface 5031 or the sample surface 5021 is kept constant at all timeseven when the stage moves or the position of the column relative to thestage shifts to the position denoted by reference numeral 5001′ or 5001″[FIG. 22( a) and FIG. 22( b)]. Therefore, differential pumping can beeffected appropriately. Thus, the charged particle beam irradiation areacan be maintained at a predetermined degree of vacuum at all times.

FIG. 23 shows another modification of the charged particle beam system.To continuously process many samples different in thickness from eachother, it is necessary to allow height adjustment to be readily effectedaccording to the thickness of each individual sample. Therefore, in thisembodiment, an elevating mechanism 5062 is provided under a samplecarrier (in this embodiment, a sample carrier using an electrostaticchuck, for example) 5063 for supporting and holding a sample, which isdisposed in a recess 5032 of the stage 5003. By vertically moving theelevating mechanism 5062 according to the height of the sample 5002, theheight of the sample surface is adjusted so that the sample surface isflush with the stage surface. The smaller the difference in heightbetween the sample surface and the stage surface, the better. The heightdifference should preferably be reduced to the order of submicrons. Forthis reason, a fine adjustment mechanism using a piezoelectric elementor the like may be provided as the elevating mechanism 5062. To processa sample 5002 having a thickness exceeding the adjustable range of theelevating mechanism 5062, the system may be arranged such that adjustingmembers 5060′ and 5061′ are provided at the sides of the sample carrier5063, and the adjusting members 5060′ and 5061′ are replaced with othersin conformity to the thickness of the sample 5002.

It should be noted that the adjusting members 5060′ and 5061′ maycomprise either a single component or two or more separate componentsaccording to the configurations of the sample 5002 and the stage 5003.It is desirable to arrange the adjusting members 5060′ and 5061′ and theelevating mechanism 5062 so that even if the sample 5002 changes in sizefrom an 8-inch wafer to a 12-inch wafer, the system can be adapted forany size of the sample 5002 simply by replacing the components inconformity to the sample size.

FIG. 24 shows another modification of the charged particle beam system.A sample 5002 is placed on the stage 5003. The sample 5002 moves withina range indicated by reference symbol L (movable range) in associationwith the movement of the stage 5003. Meanwhile, the column 5001 issecured to a frame 5014. The bottom of the column 5001 is provided witha differential pumping unit 5004 in such a manner that the differentialpumping unit 5004 surrounds the bottom of the column 5001. Differentialpumping and blowing of a high-purity inert gas are carried out in thearea between the differential pumping unit 5004 and the sample surface5021 or the top surfaces 5601 and 5611 of the plate members 5060 and5061. A container 5012 is mounted above the stage 5003 so as to coverthe movable range L of the sample 5002 completely. A small gap 5052 isprovided between the sample surface 5021 or plate members 5060 and 5061and the lower end surface of the container 5012. The high-purity inertgas blown off from the differential pumping unit 5004 enters thecontainer 5012 through the gap 5051 between the differential pumpingunit 5004 and the sample surface 5021 or the plate members 5060 and5061. Consequently, an amount of gas that is equal to the amount ofhigh-purity inert gas entering the container 5012 blows off to theoutside of the container 5012 through the small gap 5052.

With the described arrangement, the container 5012 is always filled withthe high-purity inert gas, and there is no possibility of the outsideair entering the container 5012 through the small gap 5052. Thus, theinside of the container 5012 is kept clean. Therefore, even when thesample 5002 moves within the container 5012, there is no likelihood ofthe sample 5002 being contaminated by particles, water vapor, etc.Accordingly, it becomes easy to stabilize the charged particle beamirradiation area at a high degree of vacuum. In addition, there is nolikelihood that the sample surface 5021 or the lenses in the column 5001may be contaminated. Thus, the system can be improved in reliability andoperating efficiency.

FIG. 25 shows another modification of the charged particle beam system.In this modification, a container 5015 is formed so as to completelysurround not only the sample movable range but also the stage 5003,unlike the arrangement shown in FIG. 24. The high-purity inert gas blownoff from the differential pumping unit 5004 is evacuated through avacuum pipe 5016. The arrangement of this modification also providesadvantageous effects similar to those of the modification shown in FIG.24. Furthermore, because in this modification the container 5015 coversthe stage 5003 completely, it is possible to completely eliminate thepossibility of contaminants such as particles and water vapor enteringfrom the outside. Accordingly, the system can be further improved inreliability and operating efficiency.

It should be noted that both the container 5012 in FIG. 24 and thecontainer 5015 in FIG. 25 only require to make the pressure thereinslightly higher than the atmospheric pressure so that the high-purityinert gas can be evacuated through the gap 5052 or the vacuum pipe 5016.Accordingly, containers having a simple structures such as covers willbe sufficient to serve as the containers 5012 and 5015. The provision ofthe container 5012 or 5015 has only a little effect on the size andcosts of the system.

FIG. 26 shows another modification of the charged particle beam system.This modification is provided with a container 5017 that covers thestage 5003 completely and is filled with a high-purity inert gas as inthe case of the modification shown in FIG. 25. The container 5017 iscommunicably connected with a vacuum container 5027 for loading andunloading a sample. The vacuum container 5027 is connected with vacuumpiping 5029 and high-purity inert gas supply piping 5030. Further, ablock valve 5028 is provided between the vacuum container 5027 and thecontainer 5017.

With the above-described arrangement, the charged particle beam systemaccording to this modification performs processing by the followingmethod.

First, the lid (not shown) of the vacuum container 5027 is opened, and asample 5002 to be processed with a charged particle beam is insertedinto the vacuum container 5027. Then, the lid is closed hermetically,and the vacuum container 5027 is evacuated to a predetermined degree ofvacuum through the vacuum piping 5029. Next, a high-purity inert gas issupplied through the supply piping 5030 to fill the vacuum container5027 with the high-purity inert gas. When the pressure in the vacuumcontainer 5027 has reached the same pressure as that in the container5017, the gate valve 5028 is moved in the direction of the arrow C tomove the sample 5002 into the container 5017. Then, the sample 5002 isplaced at a predetermined position on the stage 5003 by a sampletransfer mechanism (not shown). That is, after the sample 5002 has beeninserted into the vacuum container 5027, the vacuum container 5027 isevacuated to a predetermined pressure. Then, a high-purity inert gas isintroduced into the vacuum container 5027. Thereafter, the gate valve5028 is opened, and the sample 5002 is placed on the stage 5003 in thecontainer 5017 filled with the high-purity inert gas. Thereafter, thestage 5003 is moved to carry the sample 5002 to the charged particlebeam irradiation area to perform processing with the charged particlebeam.

Thus, the sample surface 5021 cleaned by evacuation is covered with ahigh-purity inert gas at all times during the transfer to the chargedparticle beam irradiation area. That is, after being cleaned byevacuation, the sample surface 5021 is not exposed to the atmosphericair. Accordingly, even when the sample 5002 is exposed to a vacuumenvironment again after being carried in the charged particle beamirradiation area, gas that may be released from the sample surface 5021is only the high-purity inert gas covering the sample surface 5021.Therefore, the released gas is evacuated within an extremely shortperiod of time, and the degree of vacuum at the charged particle beamirradiation area will not be degraded. Thus, it becomes easy to maintainthe charged particle beam irradiation area at a high degree of vacuum,and it is also possible to minimize the likelihood that the samplesurface 5021 may be contaminated.

FIG. 27 illustrates an embodiment of the evacuation path of the chargedparticle beam system. In this embodiment, piping 5013 for evacuating thecolumn 5001 is connected to an ultrahigh vacuum pump 5018. Further, thepiping 5008 for high vacuum of the differential pumping unit 5004 isconnected to an ultrahigh vacuum pump 5020. The piping 5009 for lowvacuum is connected to roughing piping of the ultrahigh vacuum pump 5020and evacuated by a roughing pump 5201. Further, as a high-purity inertgas, for example, nitrogen gas is supplied to the differential pumpingunit 5004 from a nitrogen gas source 5022 through piping 5010.

FIG. 28 illustrates a modification of the evacuation path of the chargedparticle beam system. In this modification, the piping 5013 forevacuating the column 5001 and the piping 5008 for high vacuum of thedifferential pumping unit 5004 are joined together and connected to anultrahigh vacuum pump 5018 so as to be evacuated by the ultrahigh vacuumpump 5018. Meanwhile, the piping 5009 for low vacuum of the differentialpumping unit 5004 is connected to roughing piping of the ultrahighvacuum pump 5018 and evacuated by a roughing pump 5019. With thisarrangement, the number of vacuum pumps can be reduced in comparison tothe embodiment shown in FIG. 27.

It should be noted that as the above-described ultrahigh vacuum pumps,for example, a turbo-molecular pump or an ion pump can be used. As theroughing pumps, for example, a dry pump or a diaphragm pump can be used.

FIG. 29 is a diagram showing another modification of the chargedparticle beam system, which illustrates an inert gas circulating path. Acontainer 5015 filled with a high-purity inert gas is supplied with thehigh-purity inert gas from a differential pumping unit 5004 provided ona column 5001. The supplied high-purity inert gas is evacuated from thecontainer 5015 through a vacuum pipe 5016 and pressurized by acompressor 5023. The pressurized high-purity inert gas is sent to a gaspurifier 5024, e.g. a cold trap or a high-purity filter, through piping5025. After being purified, the high-purity inert gas is sent to thedifferential pumping unit 5004 again through piping 5010 and thensupplied into the container 5015. The gas purifier 5024 need not beprovided in a case where the gas can be circulated without deterioratingthe purity.

The high-purity inert gas supplied from the differential pumping unit5004 is sucked by a differential pumping mechanism and evacuated by anultrahigh vacuum pump 5020 and a roughing pump 5201 through piping 5009for low vacuum and piping 5008 for high vacuum. Piping 5026 provided atthe evacuation side of the roughing pump 5201 is connected to theevacuation-side piping 5025 of the compressor 5023. Therefore, thehigh-purity inert gas passing through this path is also supplied to thedifferential pumping unit 5004 again through the piping 5010.

Thus, the high-purity inert gas can be circulated for reuse. Therefore,the high-purity inert gas can be economized. Further, because thehigh-purity inert gas is not discharged into the room where the presentsystem is installed, it is possible to eliminate the danger of accidentsuch as suffocation by the inert gas.

Next, a modification in which the image projection type charged particlebeam system according to this embodiment is applied to a wafer defectinspection system will be described with reference to FIG. 30.

In this modification, an electron beam E emitted from an electron gun5071 in a column 5070 for a primary optical system passes through a lensunit 5072, thereby being shaped into a predetermined sectionalconfiguration. The shaped electron beam (charged particle beam) 5050enters a Wien filter 5073. The Wien filter 5073 deflect the path of theelectron beam 5050 so that the electron beam 5050 is incidentperpendicularly or normally on the surface of a wafer 5002 as a sampleunder inspection. As a result, secondary electrons are emitted from thesample surface. The secondary electrons are accelerated by an objective5074 and travel straight through the Wien filter 5073. Thereafter, thesecondary electrons are magnified and map-projected onto a detector 5076by a lens unit 5075. The detector 5076 produces a projected image ofsecondary electrons. The image is subjected to image processing and, ifnecessary, compared with an image of another inspection region, therebyjudging whether or not there is a defect on the wafer surface. Theresult of the judgment is recorded in a given device by a predeterminedmethod and also displayed on a given device.

The arrangements and operations of a differential pumping unit 5004, acontainer 5015, vacuum piping 5008 and 5009, high-purity inert gassupply piping 5010, etc. are the same as those in the embodimentsdescribed above in connection with FIGS. 19 to 29. The high-purity inertgas flows through the container 5015 as indicated by the arrow D in thefigure and is evacuated through a vacuum pipe 5016.

This embodiment provides the following advantageous effects:

-   (1) Only a place that requires a vacuum environment can be    maintained under vacuum. Therefore, it is possible to use a stage    designed for use in the atmospheric environment and hence possible    to produce the charged particle beam system in a compact structure    at reduced costs.-   (2) It is possible to prevent particles from entering from the    atmosphere side to adhere to the sample surface and also possible to    reduce the number of opportunities for the sample to come in direct    contact with the atmospheric air. Therefore, the sample, the charged    particle beam optical system, etc. can be prevented from being    contaminated by particles, water vapor, or other contaminants.-   (3) Because the amount of gas released from the sample surface and    the surfaces of the stage components into the vacuum environment can    be reduced to a considerable extent, the charged particle beam    irradiation area can be maintained at a high degree of vacuum.-   (4) Because a stage designed for use in the atmospheric environment    can be used as it is, a hydrostatic air bearing can be used for the    stage guide. By combining with a high-precision actuator, e.g. a    linear motor, the stage for the charged particle beam system can be    improved in accuracy to the level of high-precision stages for use    in the atmospheric environment, which are used in exposure systems    and the like.

Next, an embodiment of the semiconductor device manufacturing methodaccording to the present invention will be described with reference toFIGS. 31 and 32.

FIG. 31 is a flowchart showing an embodiment of the semiconductor devicefabrication method according to the present invention. The fabricationprocess of this embodiment includes the following main steps:

-   (1) A wafer producing step for producing a wafer (or a wafer    preparing step for preparing a wafer)(step 6400).-   (2) A mask producing step for producing a mask for use in    lithography (or a mask preparing step for preparing a mask)(step    6401).-   (3) A wafer processing step for subjecting the wafer to necessary    processing treatment (step 6402).-   (4) A chip fabricating step for cutting chips from the wafer one by    one and making them operable (step 6403).-   (5) A chip inspection step for inspecting the fabricated chips (step    6404).

It should be noted that each of the above-described main steps furtherincludes some sub-steps.

Among the main steps, the wafer processing step (3) exerts a decisiveinfluence upon the performance of the resulting semiconductor devices.At this step, designed circuit patterns are stacked successively on thewafer to form a multiplicity of chips operating as memories or MPU's.The wafer processing step includes the following steps:

-   (A) A thin-film forming step for forming a thin film, for example, a    thin dielectric film serving as an insulating layer, or a thin metal    film for forming wiring patterns or electrode patterns (using CVD,    sputtering or the like).-   (B) An oxidizing step for oxidizing the thin-film layer and the    wafer substrate.-   (C) A lithography step for forming a resist pattern using a mask    (reticle) to selectively process the thin-film layer and the wafer    substrate.-   (D) An etching step for etching the thin-film layer and the    substrate according to the resist pattern (using a dry etching    technique, for example).-   (E) An ion impurity implantation and diffusion step.-   (F) A resist removing step.-   (G) A step for inspecting the processed wafer.

It should be noted that the wafer processing step is repeated the numberof times equal to the number of necessary layers to producesemiconductor devices that are operable as designed.

FIG. 32 is a flowchart showing the lithography step, which is at thecore of the wafer processing step in FIG. 31. The lithography stepincludes the following steps:

-   (a) A resist coating step for coating a resist over the wafer having    a circuit pattern formed thereon at the preceding step (step 6500).-   (b) A step for exposing the resist (step 6501).-   (c) A development step for developing the exposed resist to obtain a    resist pattern (step 6502).-   (d) An annealing step for stabilizing the developed resist pattern    (step 6503).

The above-described semiconductor device producing step, waferprocessing step and lithography step are well known. Therefore, nofurther description thereof will be needed.

The use of the defect inspection method and defect inspection systemaccording to the present invention in the inspection step (G) allowseven semiconductor devices having fine patterns to be inspected withfavorably high throughput. Accordingly, it becomes possible to perform100% inspection and hence possible to improve the product yield and toprevent shipment of defective products.

The inspection procedure at the inspection step (G) will be describedbelow.

Generally, a defect inspection system using an electron beam is costlyand has low throughput in comparison to other process systems. In thepresent state of the art, therefore, the electron beam defect inspectionsystem is used after an important fabrication step that is considered tobe most in need of inspection [e.g. etching, film deposition (includingplating), or CMP (Chemical/Mechanical Polishing) planarizationtreatment].

A wafer to be inspected is carried to an ultraprecision X-Y stagethrough an atmosphere transfer system and a vacuum transfer system andaligned on the stage. Thereafter, the wafer is secured by anelectrostatic chuck mechanism or the like and then subjected to defectinspection or other processing according to the following procedure(i.e. the inspection flow shown in FIG. 33). First, the confirmation ofthe position of each die and the detection of the height of eachposition are performed according to need with an optical microscope, andinformation thus obtained is stored in a memory (step 7001). Inaddition, the optical microscope acquires an optical microscopic imageof a region where defect inspection or the like is to be performed. Theimage thus obtained is used for comparison with an electron beam image.Next, information concerning a recipe is selected according to the typeof inspection and the type of wafer (e.g. according to which step hasbeen carried out just before the present inspection step, and whetherthe wafer size is 20 cm or 30 cm) and input to the system (step 7002).Then, designation of an inspection position (step 7003), setting of theelectron optical system and setting of inspection conditions, and soforth are made (step 7004). Thereafter, a defect inspection is carriedout in real time under normal circumstances while image acquisition isbeing performed (step 7005). Thus, inspection based on cell-to-cellcomparison, die-to-die comparison, etc. is performed by a high-speedinformation processing system having an algorithm, and the result of theinspection is output to a CRT or the like and stored in a memoryaccording to need (step 7006). Defects include particle defects, shapeabnormalities (pattern defects), and electrical defects (disconnectionand conduction failures of wiring patterns or vias, etc.). The systemcan also automatically distinguish between these defects and classifydefect sizes and killer defects (serious defects that make the chipimpossible to use) in real time. The detection of electrical defects iseffected by detecting a contrast abnormality. For example, a conductionfailure position is charged positively by electron beam irradiation(about 500 eV) under ordinary circumstances and consequently reduced incontrast. Therefore, it can be distinguished from a normal position.Electron beam irradiation devices used in this case include, in additionto an electron beam irradiation device for ordinary inspection, anelectron beam emitter (a thermionic emitter or a UV/photoelectronemitter) for emitting an electron beam of low energy provided to enhancethe contrast by an electric potential difference. Before the electronbeam for inspection is applied to a region under inspection, theelectron beam of low energy is emitted and irradiated to the regionunder inspection. In the case of the image projection type electron beaminspection system, a conduction failure position can be chargedpositively by irradiation with the electron beam for inspection.Therefore, in such a case, the device for generating an electron beam oflow energy need not additionally be provided, depending upon thespecifications. It is also possible to detect a defect from a differencein contrast produced by applying a positive or negative electricpotential to a sample, e.g. a wafer, with respect to the referenceelectric potential (such a contrast difference is produced owing to thedifference in electric flowability according to whether it is theforward direction or the backward direction of the device). Thistechnique can also be used for line width measurement and alignmentaccuracy measurement.

As an inspection method for detecting electrical defects of a sampleunder inspection, it is also possible to make use of the fact that aportion that should be electrically insulated shows a difference in theelectric potential measured when the portion is electrically insulatedor when it is conducting.

First, an electric charge is given to the sample in advance so thatthere is a difference in electric potential between a portion thatshould be electrically insulated and a portion that should beelectrically insulated but is conducting for some reason. Thereafter, abeam is applied to the sample by the method according to the presentinvention, thereby obtaining data containing the electric potentialdifference. Then, the data thus obtained is analyzed to detect the factthat the portion that should be electrically insulated is conducting.

In the foregoing embodiments, when an electron beam is generated, atarget substance is floated by the proximity interaction(electrification of particles near the surface) and drawn to ahigh-electric potential area. Therefore, an organic material acting asan insulating material is deposited on the surfaces of variouselectrodes used to form and deflect the electron beam. The insulatingmaterial gradually deposited on the surface of an electrode as theelectrode surface is electrically charged has an adverse effect on theformation of the electron beam or on the deflecting mechanism.Therefore, the deposited insulating material has to be removedperiodically. Periodic removal of the deposited insulating material iscarried out as follows. A plasma of hydrogen, oxygen, fluorine, or acompound containing such a substance, e.g. HF, O₂, H₂O, or C_(m)F_(n),is produced in a vacuum by utilizing an electrode in the vicinity of anarea where the insulating material is deposited, and the plasma electricpotential in the space is maintained at an electric potential at whichsputtering occurs on the electrode surface (several kV, e.g. 20 V to 5kV), thereby removing only organic substances by oxidation,hydrogenation, or fluorination.

It should be noted that the present invention is not necessarily limitedto the foregoing embodiments. For example, the elements of the describedembodiments may be combined together as desired.

The term “inspection” as used in this application means not only thedetection of presence of failures, e.g. defects, but also the evaluationof the inspection result.

The entire disclosure of Japanese Patent Applications Nos. 2001-2722filed on Jan. 10, 2001, 2001-75865 filed on Mar. 16, 2001, 2001-92748filed on Mar. 28, 2001, 2001-125349 filed on Apr. 24, 2001 and2001-189325 filed on Jun. 25, 2001 including specification, claims,drawings and summary is incorporated herein by reference in itsentirety.

1. An electron beam inspection system comprising: an electronirradiation gun for irradiating a primary electron beam to a surface ofa sample; stage for supporting and moving the sample in a direction; asecondary optical system for magnifying and projecting secondaryelectrons generated from the sample by irradiating the primary electronbeam to form an image of the surface of the sample; a TDI (Time DelayIntegration)-CCD (Charged Coupled Device) for detecting the secondaryelectrons and integrating electric charges converted from the detectedsecondary electrons in a surface array direction of the TDI-CCD; and amagnetic lens for rotating an image formed by the secondary electronspassing the magnetic lens such that a scanning direction of the sampleas scanned by moving the stage coincides with an integration directionfor integrating the electric charges in the surface array direction ofthe TDI-CCD by controlling the intensity of magnetic field which isproduced by the magnetic lens and applied to the secondary electrons. 2.An electron beam inspection system according to claim 1, wherein themagnetic lens is positioned between a lens in a final stage of theoptical system and a microchannel plate placed in a preceding stage ofthe TDI-CCD.
 3. An electron beam inspection system according to claim 2,wherein the magnetic lens is disposed at a crossover position closest tothe microchannel plate.
 4. An electron beam inspection system accordingto claim 1, wherein the magnetic lens is disposed at an image-formationposition closest to a final-stage lens of the optical system on a sideof the final-stage lens remote from the microchannel plate.
 5. A devicefabrication method using the electron beam inspection system accordingto claim 1.